HIV infection among the mentally ill is estimated to be at least eight times the prevalence in the general population. Psychiatric patients may also be disproportionately vulnerable to other sexually transmitted infections (STIs), but this has not been well studied. We sought to characterize the prevalence and correlates of STIs in a sample 80of psychiatric outpatients (N = 464). Over one-third of the sample (38%) reported a lifetime history of one or more STIs. Multivariate analyses showed that, relative to those without an STI history, patients with a lifetime STI history were more knowledgeable about HIV, expressed stronger intentions to use condoms, and perceived themselves to be at greater risk for HIV. However, those with a past STI were also more likely to report sex with multiple partners and reported more frequent unprotected sex in the past 3 months. Treatment for an STI may increase HIV knowledge and risk reduction motivation, but does not necessarily lead to changes in sexual risk behavior among psychiatric patients. Findings highlight the need for STI/HIV risk reduction interventions in psychiatric settings, particularly for patients with high-risk profiles.