Adults with severe mental illness (SMI) are disproportionately affected by HIV/AIDS. This study describes the frequency and associated factors of HIV testing among psychiatric outpatients (N = 150) in a small Northeastern city. A structured clinical interview assessed demographic, psychosocial, behavioral, and psychiatric factors. In the past year, 41% of participants were HIV tested. A hierarchical linear regression model revealed the following multivariate correlates: lower educational attainment, HIV risk behavior, greater social support, homelessness, non-psychotic disorder, borderline personality disorder, and greater treatment utilization. Psychiatric factors remained significant correlates of HIV testing after accounting for psychosocial and behavioral factors. Although HIV testing occurred among a substantial proportion of participants, 45% of individuals who engaged in HIV risk behavior were not tested in the past year. Adults with SMI are in need of interventions promoting routine HIV testing and risk-reduction counseling.