Objective: To determine the prevalence and analyse the characteristics and causes of malnutrition among inpatients in an HIV highly endemic area. Design: Prospective cross-sectional study. Setting: Department of Internal Medicine, University Hospital, Bujumbura, Burundi. Subjects: 226 adult inpatients. Main outcomes measures: Evaluation of nutritional status using anthropometry. Degree of malnutrition de®ned by the percentage of body weight loss (BWL), calculated by reference to the usual body weight. Results: Among the 226 patients recruited (mean age: 34.4 AE 11.9 y, M:F sex ratio: 1.72), 102 (45.1%) were HIV seropositive. 62 (60.8%) of these HIV seropositive were AIDS cases. The AIDS de®ning criterion was wasting syndrome' for 25 (40.3%) and opportunistic infection (OI) for 37 (59.7%) including 34 cases of tuberculosis (TB). The nutritional status of 119a226 patients (52.7%) was normal (BWL 10%). Moderate malnutrition (10% BWL 20%) was observed in 47 (20.8%) and severe malnutrition (BWL b 20%) was observed in 60 (26.5%). HIV seroprevalence and, among HIV seropositive subjects, the percentage of AIDS cases increased according to decreasing level of nutrition (Chi2 for trends: P`0.001 in both instances). The fat free mass mass of malnourished subjects was lower and the fat body mass was higher among HIV seropositive subjects than HIV seronegative subjects. Among HIV seropositive subjects, malnutrition was associated with TB (P`0.001) and dysphagia (P`0.05). Among HIV seronegative subjects, malnutrition was associated with decreased food availability (P`0.003) and TB (P`0.05). One week after admission, the mortality rate was higher among HIV seropositive subjects (10.8%) than seronegative subjects (2.4%, P 0.009). Other factors associated with death were decreased fat free mass (P`0.01) and tricipital skinfold thickness (P`0.04). Conclusions: The prevalence of malnutrition is high among the inpatients investigated. Main factors are HIV infection and TB. Strategies adapted to the African context should be developed to prevent, detect and treat malnutrition and associated factors, particularly among HIV seropositive subjects.