To ascertain the degree of HIV-risk knowledge among patients attending a downtown program and to identify the extent of high-risk behaviour for HIV infection. A total of 151 patients were selected at the Calgary Community Mental Health Clinic (N = 110) and the nearby Self Help Association (N = 41). Most of the subjects were being treated for either schizophrenia (n = 69), bipolar disorder (n = 37), or unipolar mood disorder (n = 35). Questionnaires included a 10-item instrument that assessed subjects' knowledge about HIV or AIDS and another 10-item tool that assessed the high-risk situations patients might have encountered over the past month or past year. Although the percentage of subjects erring on questions about AIDS knowledge was smaller when compared with previous studies, a significant number of subjects believed that one could acquire AIDS by donating blood, and 25% did not think that having only one unsafe sexual contact would make them vulnerable to HIV infection. At least 50% of the participants have had sex with at least one partner in the past year, and 33% of the participants indicated that they would not insist that they or their partners wear a condom. This Canadian study confirms the need for psychiatrists and mental health workers to continue to explore high-risk behaviour in the chronic mentally ill population and to further educate these patients through the development of prevention and risk-reduction strategies.