Strict adherence to the prescribed drug regimen is one of the most important predictors of success in the antiretroviral therapy of HIV infection. Ideally, patients should learn to optimise their drug adherence before they start antiviral therapy. This study evaluated the predictive role of adherence during the first four weeks of treatment for mid-term treatment outcome. Adherence was evaluated using electronic dosing systems during the first 25 days of therapy in 66 drug-naïve patients starting a new antiretroviral therapy. Treatment outcome (HIV-RNA suppression) was evaluated at week 24 of treatment. Good adherence (>95%doses taken) was associated with better rates of viral suppression (77% vs. 44% Patients with HIV-RNA below 50 copies/ml). Specific education programmes targeted at the achievement of optimal adherence during the first few weeks of therapy might result in better treatment results.