We describe three related studies of possible aetiological risk factors for sexually transmitted diseases (STDs) in men attending an STD clinic. In this paper we present the results for a variety of social and demographic variables traditionally associated with STD. In contrast to the results in the next two papers, these were largely negative. Occurrence rates of overall STD or of hepatitis, syphilis, gonorrhoea, or non-specific urethritis (NSU) had no aetiologically relevant association with age, nationality, marital status, social class, occupation, non-sexual social contact, drug abuse, or aggressive attitudes and behaviour. Gonorrhoea, however, was the only STD which correlated with alcohol abuse and with eating out rather than at home. We conclude that, with the possible exception of gonorrhoea, social factors contribute little to the distribution of STD risk within the study population.