This is a two-arm randomized controlled trial (RCT) for 308 seriously mentally ill adults (SMI) engaging in risky sexual and/or drug use behavior, comparing a brief HIV primary and secondary prevention intervention [Skills building and Motivational Interviewing (SB-MI) to Care as Usual (CAU)]. The study setting is a large urban safety net Medical Center and outcomes will be measured at 3, 6, and 12 months. The SB-MI intervention (3 sessions + booster) was initially developed as the experimental condition in an R34 pilot project which demonstrated its feasibility and promise. For the proposed project, the investigators will recruit a larger sample which includes men and women with and without HIV, from various ethnic and racial groups, sexual orientations and housing arrangements, as well as a range of psychiatric disorders and functional capacities. In this way the investigators can more rigorously demonstrate the promise of SB-MI with SMI. The investigators will also conduct a sub-study after the 6 month follow-up to examine the impact at 12 months of an additional booster session for SB-MI participants. The investigators specific aims are: