Pica was recognized in 25.8 percent of a population of 991 institutionalized mentally retarded adults. Food pica accounted for 5.4 percent, nonfood pica for 16.7 percent, and combination food and nonfood pica for 3.7 percent of the population. Pica became less frequent with increasing age, related to a reduction in the incidence of nonfood pica. Food pica was not age-related. Low IQ was associated with a high frequency of nonfood pica. The items consumed were classed into 29 nonfood and 7 food categories. Some medical complications such as intestinal obstruction and surgery secondary to foreign body ingestion occurred only in those with pica. Gastrointestinal parasites occurred more frequently in individuals with pica.