We conducted a randomised clinical trial to test the efficacy of an enhanced version of an intervention previously shown to reduce HIV sexual risk behaviours among men with severe mental illness. One-hundred-and-forty-nine subjects aged 18-59 years were randomly assigned to the experimental or control conditions. Sexual risk behaviours were assessed every three months for 12-months. The primary analysis compared experimental and control groups with respect to sexual risk behaviours with casual partners as measured by the Vaginal Episodes Equivalent (VEE) score. Additional analyses included comparison of VEE scores of those men sexually active in the three months prior to baseline and the proportion of condom-protected sexual acts with casual partners. There were no significant differences in sexual risk behaviours with casual partners between experimental and control subjects. Additional analyses demonstrated a trend toward sexual risk reduction at six months post-intervention (p=0.06) but not at 12 months. These results may reflect a lack of efficacy or a true reduction in risk that the trial was underpowered to detect at the 0.05-level. If there was a true reduction in risk, it was not maintained after the initial six months.