The aim of this study was to evaluate fat absorption in HIV-positive (HIV+) patients in different phases of HIV infection using a 14C-triolein breath test. We distributed 47 HIV+ patients according to the 1993 Centers for Disease Control Revised Classification: 20 in Group 2 (A1 or A2) and 27 in Group 3 (B1, B2, A3, B3, or C). Ten HIV-negative healthy subjects comprised the control group (Group 1). All individuals underwent a 14C-triolein breath test. Parasitic infection was evaluated through three stool exams, including Cryptosporidium and Isospora investigation. The median value of cumulative 6 hours' 14C excretion expressed as percentage of the 14C given as triolein was significantly higher in Group 1 (8.4%) than Group 2 (5.5%) or Group 3 (3.4%), p = 0.04 and p << 0.01, respectively. Fat malabsorption was found in 25% of Group 2 individuals, 52.6% of those without diarrhea in Group 3, and was correlated with CD4+ lymphocyte counts (p << 0.01). Fat malabsorption is a common feature in advanced stages of HIV infection, even in the absence of diarrhea and is also present in asymptomatic HIV+ patients. These findings suggest that malabsorption is an early event in HIV-infected individuals and is correlated with the degree of immunosuppression.