This study described HIV prevalence, risk behaviors, health care use, and mental health status of male-to-female and female-to-male transgender persons and determined factors associated with HIV. We recruited transgender persons through targeted sampling, respondent-driven sampling, and agency referrals; 392 male-to-female and 123 female-to-male transgender persons were interviewed and tested for HIV. HIV prevalence among male-to-female transgender persons was 35%. African American race (adjusted odds ratio [OR] = 5.81; 95% confidence interval [CI] = 2.82, 11.96), a history of injection drug use (OR = 2.69; 95% CI = 1.56, 4.62), multiple sex partners (adjusted OR = 2.64; 95% CI = 1.50, 4.62), and low education (adjusted OR = 2.08; 95% CI = 1.17, 3.68) were independently associated with HIV. Among female-to-male transgender persons, HIV prevalence (2%) and risk behaviors were much lower. Most male-to-female (78%) and female-to-male (83%) transgender persons had seen a medical provider in the past 6 months. Sixty-two percent of the male-to-female and 55% of the female-to-male transgender persons were depressed; 32% of each population had attempted suicide. High HIV prevalence suggests an urgent need for risk reduction interventions for male-to-female transgender persons. Recent contact with medical providers was observed, suggesting that medical providers could provide an important link to needed prevention, health, and social services.