BACKGROUND: People with a parent with type II diabetes have an increased risk of the disease. There is increasing evidence for the possibility of prevention, particularly by attaining and maintaining normal weight and adequate levels of physical exercise. No prior studies have reported awareness of risk and prevention in this high-risk group. AIM: To explore beliefs about personal risk of diabetes and prevention in people with a parent with type II diabetes. DESIGN OF STUDY: A total of 254 adults with type II diabetes were identified from five randomly selected practices in south London. Self-report questionnaires were sent to 152 eligible offspring of these patients. A total of 105 of the offspring returned the self-report questionnaires and participated in the study. SETTING: Five randomly selected practices in south London. METHODS: Patients with type II diabetes in five randomly selected practices in south London were asked if we might contact their offspring. One randomly selected offspring (over 18 years of age) from each family completed a self-report questionnaire. RESULTS: Of 254 adults with type II diabetes 152 had eligible offspring. A total of 105 (69%) of the offspring participated in the study. A total of 69 (66%) of these offspring believed their personal risk of developing diabetes was 'low'. At least 28 (28%) and maybe as many as 73 (70%) underestimated the risk of diabetes in offspring. Compared with the number thinking their current risk was low significantly more (95 versus 69) thought that their risk would be low if neither of their parents had diabetes. Fifty-seven (54%) thought prevention was possible. Sixteen thought taking more exercise was important for prevention and only seven thought that weight control was important. Many had good general knowledge about diabetes and its complications but awareness of the relationship between diabetes and cardiovascular disease was poor. CONCLUSIONS: People with a parent with type II diabetes are usually aware that they have an increased risk of diabetes. However, they often underestimate that risk and know little about potentially useful preventive strategies. They need accurate information about these matters if they are to reduce their risk of diabetes and its complications.