Objectives: To evaluate adherence, side effects and efficacy of a modality of highly active antiretroviral therapy (HAART) in HIV-infected patients., Methods: In a cohort, prospective study, 65 previously treated patients received stavudine plus lamivudine plus nelfi-navir. Fifty-three participants (81%) had a history of intravenous drug use. Patients were evaluated at 3-month intervals. The association of adherence with demographic variables, hepatitis C virus infection, number of stopped antiretroviral regimens, HIV RNA level, CD4 cell count, and adverse effects to drugs was assessed. Results: After a median follow-up of 12 months, 30 participants (46%) showed adequate adherence in all visits, An association was observed between adherence and female sex: 18 of 47 men (35%) vs, 12 of 18 women (67%) presented adequate adherence in all visits (P=0.0416), An association was also observed between adherence and low baseline HIV RNA level (P=0.0229). Discontinuation of treatment took place because of refusal to take medication in 11 participants (17%) and because of side effects in seven participants (11%), Undetectable HIV RNA level was achieved in 26 patients (40%) at 3 months and in lower percentages at months 6, 9 and 12, Conclusions: Overall adherence to the employed HAART regimen was poor. Female sex and low baseline HIV RNA were associated with better adherence. Refusal to take medications and side effects were the main reasons to stop therapy. At 3 months' follow-up, virological efficacy was achieved in 40% of patients. (C) 2000 The British Infection Society.