Suicide and suicidal behavior are serious social and public problems in China and around the world, particularly in children and adolescents 
. According to the 2004 World Health Organization (WHO) Mortality Database, the suicide rate of youth aged 15–19 in China is 4.0 per 100,000 with a gender ratio of 0.7
females), which is a little lower than that in Japan (6.4 in total, a male to female ratio of 2.3
1) where suicide numbers are as many as those in China 
. As to children aged 5–14, their suicide rate increased from 0.7 to 0.9 per 100,000 for males and remained 0.8 per 100,000 for females in the 1990s, much higher than that in Japan (0.5 for males and 0.3 for females) 
. Previous studies have also showed that suicide rate increased at the late teens and continued to rise until the early twenties 
. In addition, the prevalence of nonfatal suicidal behavior, including suicide thoughts, suicide plans, deliberate self-harm, and attempted suicide, are also common in 15–24 year olds adolescents 
. In the United States, the average rate of adolescents reporting suicide attempts in the past one year is 6.4%, 12.4% reporting suicide plans, and 19.3% reporting suicide thoughts 
. In rural areas of China, the prevalence of suicide ideation, plans and attempts among adolescents are 19.3%, 10.5%, and 7.0%, respectively 
. Although only a small proportion of suicide attempters complete suicide eventually, suicide attempts are significant predictors and indicators of subsequent completed suicide 
. As a result, understanding youth suicide and suicide behavior and finding useful prevention strategies are extremely urgent.
One of the most concerned risk factors for suicide and suicidal behavior is aggression/violence. First of all, they have a common basis in pathophysiology, the abnormal serotonergic system. For example, lower level of cerebrospinal fluid 5-hydroxyindolacetic acid is not only associated with the increased risk of future suicide among adolescents, but also with the severity of lifetime aggression 
On the other hand, psychologically speaking, aggression is an important diathesis part of suicide behavior according to the stress-diathesis model proposed by John Mann 
. Individuals with this diathesis might be likely to experience more suicidal feelings and thoughts, and to be more impulsive. He also hypothesized that the risk for suicidal behavior was determined both by a psychiatric illness and by the diathesis, and the diathesis or trait-like predisposition was more important than the severity of the illness in predicting suicidal behavior.
Previous studies in both high-risk individuals and school-based populations have found that trait aggression may act as a predictor of future suicide and elevate the risk for suicidal behavior. For example, Keilp JG et al's study found that it was aggressiveness that held the most importance in predicting suicidal behavior when stratifying by borderline personality disorder, and that should be viewed as the ideal target for further research on suicidal behavior and for the clinical assessment of suicide risk 
. Conner et al. have concluded that both reactive aggression and proactive aggression is associated with suicidal behavior among substance-dependent patients 
. Swogger et al's study has further suggested that aggression acts as an important mediator of the relationship between childhood physical abuse and suicide attempts among criminal offenders, supporting the importance of aggression treatment in suicide prevention programs. 
. Furthermore, school-based studies have revealed: (1) that suicide-only adolescents have higher levels of overt and covert aggression than non-violent and non-suicide ones, and higher levels of covert aggression than violent-only ones; (2) that those who scored higher on reactive aggression had a greater risk for suicide behaviors than those with higher score on proactive aggression 
. Finally, as a behavioral marker of a high level of aggression, violent method accounts for the majority of suicides in the United States, especially firearms 
Additionally, evidence to date indicating the possibility that interventions directed at aggression may reduce the risk for suicidal behavior is numerous. For example, Lubell suggested a promising strategy of integrating suicide and violence prevention based on their shared influences to maximize the effectiveness and efficiency of prevention programs 
. Other researchers also found that violent behavior in schools acts as a predictor of suicidal ideation, plans, and attempts among adolescents and stated the importance of combining violence and suicide prevention efforts 
. A Korean researcher tested the effectiveness of an integrated suicide-violence prevention program through a case-control study and found that this integrated program increased self-esteem and reduced aggression and suicidal behavior scores significantly 
On the basis of the above-mentioned studies, it must be concluded that the relationship between aggression/violence and suicidal behavior is without a doubt in the West. In China, however, there are no large studies investigating the effect of aggression on suicidal behavior. But we cannot replicate findings in the West directly to the Chinese population because suicidal behavior in China has its own characteristics due to different cultural, political, and social climates, and access to lethal methods for suicide and health care 
. For example, the male to female gender ratio for suicide in China (1
1.3) is much lower than that of western countries, where the typical male to female ratio is between 2
1 and 4
. Also, neither the main cause nor the most common method of suicide in China is consistent with those in most western countries (mental health disorders vs. family conflicts; violent methods like firearm vs. nonviolent methods like pesticide poisoning) 
. Discrimination against females, no religious or legal injunctions against suicide, the availability of suicide means (e.g. pesticides) and a longstanding tradition of using suicide as a fighting mean against parents or unfair things may partly explain those unique features 
. As a result, it is risky to apply the findings about the association between aggression and suicide behavior in western population directly to adolescents in China.
Moreover, Shaffer concluded that aggressive/violent outbursts and depression or withdrawal were two characteristics of people who were more vulnerable to suicide tendencies in 1970s 
. According to this theory, most of suicide in the West is of the latter type since mental illness, substance use disorders and alcohol use disorders are factors that most consistently associated with suicide. In China, however, a recent study about the psychological strain theory of suicide among Chinese adolescents has formed a challenge to the psychiatric model that is well-established in the West 
. Besides, Cui's study among Chinese adolescents has revealed that the special problems related to peer relationships, especially physical fighting and lack of peer association, were significantly related to suicide behavior 
. A suicidal temperament/personality theory has suggested that impulsiveness, aggressiveness, anger, and hostility are crucial predispositions mediating suicidal behavior 
. As a result, we need to study the relationship between aggression and suicide to better understand the risk factors for suicide and suicide behavior in China. And further investigations should be done to explore how trait aggression predicts suicidal behavior among Chinese adolescents.
The aim of the present study was to explore which forms of trait aggression were associated with suicidal behavior, as well as to reestimate the prevalence of suicide ideation, plans and attempts among adolescents of urban areas in China. . Based on literatures reviewed above, we hypothesized that physical aggression, anger, and hostility would be risk factors of adolescents' suicidal behavior after adjusting for various risk factors.