Hyperlipidemia has been frequently recorded as a side effect of treating HIV patients with protease inhibitors (PI). This study was initiated to analyze the modifications on blood lipids in HIV-patients receiving PI and the safety and efficacy of the treatment with fenofibrate. Total (TC) and HDL-cholesterol, triglycerides (TG), and CD(4)(+) T-cell counts were measured in 30 HAART-naive patients (Group I) before and after PI introduction. In a second phase of the study, the effects of fenofibrate on lipids, CPK, CD(4)(+), and viral load were determined in 13 patients (Group II) with elevated TC or TG. In Group I, 60% of the patients showed TC or TG elevations. Average increments of 31% and 146% in TC and TG respectively (p<0.0006 and p<0.0001) were observed. In Group II, fenofibrate treatment was associated with decrements of 6.6% (TC) and 45.7% (TG) (p=0.07 and 0.0002) and no modifications on CPK, CD(4)(+), and viral load. In conclusion, hyperlipidemia is common during the treatment of HIV with protease inhibitors, and fenofibrate appears to be an effective and safe choice for its treatment.