Persons with mental disorders may lack the knowledge, skills, and social networks that help limit the spread of HIV by reducing risk behaviors. Nationally representative data from the 1999 U.S. National Health Interview Survey were used to estimate the prevalence of HIV risk behaviors among civilian noninstitutionalized adults with and without at least one of three psychiatric conditions (depression, generalized anxiety disorder, and panic attacks) in the previous 12 months. Relative to adults without these mental disorders, adults with a mental disorder (8.8% of adults nationally) were more likely to have engaged in HIV risk behaviors since 1980 (5.5% vs. 1.6%). Adults with a mental disorder were also more likely to report a high or medium chance of becoming infected, were more likely to have been tested for HIV infection, and were more likely to expect to be tested within the next 12 months.