We used a standardized screening tool to examine frequency of depression and its relation to antiretroviral medication adherence among HIV-infected persons on highly active antiretroviral therapy (HAART) in the Study to Understand the Natural History of HIV/AIDS in the Era of Effective Therapy (SUN Study). This is a prospective observational cohort of 700 HIV-infected patients enrolled between March 2004 and June 2006 in four U.S. cities, who completed a confidential audio computer-assisted self-interview [ACASI] with behavioral risk and health-related questions at baseline and 6-month follow-up visits, including the nine-question PRIME-MD depression screener and a validated 3-day antiretroviral adherence question. Among 539 eligible participants receiving HAART, 14% had depression at baseline (22% women, 12% men). In multivariable analysis using generalized estimating equations (GEE) to account for repeated measurements through 24 months of follow-up, persons who reported depression on a given ACASI were twice as likely to report nonadherence to antiretrovirals on the same ACASI (Odds ratio [OR] 2.02, 95% CI: 1.15, 3.57] for mild/moderate depression versus none); such persons were also less likely to have HIV viral load<400 copies/mL. Self-administered computerized standardized screening tools can identify at-risk individuals with depression who may benefit from interventions to improve antiretroviral adherence.