BACKGROUND Effective virological suppression with HAART is dependent on strict adherence to therapy. Compliance with therapy is influenced by clinical and psychosocial factors. METHODS We performed a retrospective study investigating determinants of effective virological suppression, defined as <400 RNA at 11-13 months of HAART, in an urban indigent population. The study included 366 new patients presenting for care to the Thomas Street Clinic, Houston, Texas, between April and December 1998. Median age, CD4 count, and viral load (VL) of the study population were 37.5 years, 189 cells/mm(3), and 53,000, respectively. Thirty-nine percent had AIDS, 20% had cocaine-positive drug screens, and 64% were antiretroviral naïve. Two hundred and sixty-seven patients were started on HAART. Thirty-four percent showed virological suppression. RESULTS In multivariate analysis, adherence to HAART, care by experienced primary provider, baseline VL <100,000 copies/mL, age >35 years, and no active substance use were associated with virological suppression. Rates of virological suppression with HAART are unacceptably low in this urban indigent population. CONCLUSIONS Low rates of virological suppression are primarily due to lack of adherence rather than late utilization of care among ethnic minorities. Single protease-inhibitor-based antiretroviral therapy does not appear to be highly active in this patient population.