Infections with gastrointestinal parasites may be a major threat to lemurs kept in captivity, as they are a common cause of diarrhea. In this study, fecal egg count patterns and clinical signs associated with gastrointestinal nematodes were assessed for 12 mo in 40 lemurs kept under different husbandry and climatic conditions at two sites in Madagascar. Involved species were black-and-white ruffed lemurs (Varecia variegata), eastern grey bamboo lemurs (Hapalemur griseus), greater bamboo lemurs (Prolemur simus), red-bellied lemurs (Eulemur rubriventer), common brown lemurs (Eulemur fulvus), crowned lemurs (Eulemur coronatus), and Sclater's black lemurs (Eulemur macaco flavifrons). At site 1 (Tsimbazaza Zoological Park), lemurs were kept in small enclosures with daily cleaning of the cement soiling and without routine anthelmintic program, whereas at site 2 (Ivoloina Zoological Park), lemurs received routine anthelmintic prophylaxis and were housed in small enclosure with daily cleaning of sandy soil enclosures. A total of five genera of nematode eggs from the orders Strongylida, Oxyurida, and Enoplida were recovered and identified from 198 out of 240 samples (83%) at site 1 and 79% (189 out of 240) at site 2 with the use of a modified McMaster technique. Significant differences were found for parasites from the order Strongylida between the two sites. The differences may be due to climate conditions and the presumed life cycle of these parasites. No significant differences were found for parasites from the other orders. No significant differences were noted between sexes or between seasons. No clinical signs of parasitic gastroenteritis were seen in either lemur collection.