Morbidity, mortality, and drug treatment data suggest that methamphetamine use is on the rise. Based on research findings of the sexual behaviors of methamphetamine-using injection drug users, we chose to examine the relationship between methamphetamine use during sex and risky sexual behaviors and human immunodeficiency virus (HIV) seropositivity among clients of publicly funded HIV testing sites in California who reported never injecting drugs. We found that among gay, bisexual, and heterosexual men and heterosexual women, users of methamphetamines reported more sexual partners than non-methamphetamine users. Among heterosexuals, a greater percentage of methamphetamine users than nonusers participated in anal intercourse. Methamphetamine use was independently related to decreased condom use during vaginal and anal intercourse, prostitution, and sex with known injection drug users. In addition, methamphetamine users were more likely to have had a sexually transmitted disease. When controlling for race or ethnicity; age; exposure to possibly infected blood or blood products; and the use of cocaine, alcohol, or marijuana during sex, methamphetamine-using bisexual men were more likely to test positive for HIV than those reporting no history of methamphetamine use. Our data suggest that noninjection methamphetamine use is related to increased, unprotected sexual activity and the risk of contracting sexually transmitted diseases, including HIV.