This study examined whether training women living with a severe mental illness to be assertive in sexual situations would decrease their risk for HIV infection. Twenty female outpatients were randomly assigned to either a 10-session assertiveness training intervention or a waiting-list control condition. All participants completed measures of HIV-related information, motivation, skills, and sexual risk behavior pre- and postintervention and at 2- and 4-month follow-ups. Compared with controls, women in the intervention group increased their assertiveness skill, HIV knowledge, and frequency of condom-protected intercourse. It is concluded that assertiveness training for women living with a severe mental illness can serve as 1 part of a comprehensive HIV-risk-reduction program for this vulnerable population.