ObjectiveTo determine whether specific intestinal parasites are associated with HIV infection in Tanzanian children with chronic diarrhea.DesignA prospective, cross-sectional study.SettingMuhimbili University College of Health Sciences, Dar es Salaam, Tanzania.SubjectsAll children aged 15 months to 5 years admitted with chronic diarrhea, and age-matched controls.MethodsStandardized history, physical examination, HIV serology, and stool parasitology were evaluated for all subjects. We compared three groups: HIV-infected and non-HIV-infected children with chronic diarrhea and controls without diarrhea.Main outcome measuresFecal parasites and nutritional status.ResultsChronic diarrhea accounted for one-quarter of all cases of diarrheal disease in the defined age range, and children with chronic diarrhea were severely malnourished. Forty per cent of subjects with chronic diarrhea were HIV-seropositive. Although intestinal parasites were detected in approximately 50% of all three groups, diarrheagenic parasites were detected in up to 40% of children with chronic diarrhea. Blastocystis hominis was detected only in HIV-infected patients.ConclusionsHIV infection was common in children with chronic diarrhea, and parasitic agents of diarrhea may be important in children with chronic diarrhea both with and without HIV infection in this setting. B. hominis was more frequent in HIV-infected children. The immunocompromising effects of severe malnutrition may have diminished the difference between HIV-infected and non-HIV-infected children.