Serologic surveys for Toxocara canis and Strongyloides sp., as well as stool examinations for intestinal parasites, were conducted in a home for mentally retarded adults. Evidence of parasitic infection was found in 30 (28.3%) of 106 residents; nine (8.5%) had positive toxocaral serology (enzyme-linked immunosorbent assay[ELISA]), 1 (0.9%) had positive serology for Stronglyoides sp. (ELISA), and 21 (19.8%) had parasites in stool (including Stronglyoides stercoralis in the patient with positive serology). Most of the residents with positive toxocaral serology lived in the same apartment and used to play with dogs. Parameters found to be significantly associated with positive toxocaral serology were pica behavior and eosinophilia (P less than 0.05). Mental retardation requiring institutionalization appears to be a risk factor for toxocariasis and other parasitic infections in adults as it is for children.