Parasitic infection is highly prevalent throughout the developing countries of the world. These infections are the major problem in rehabilitation centers for the mentally retarded. There have been many reports about the prevalence of parasitic infection among different groups of people in Iran; however, the epidemiological data in intellectual disability (ID) individuals are rare and there are no such data from northern Iran. The aim of the present study was to determine the incidence of intestinal parasitic infections among the inhabitants of rehabilitation centers of Mazandaran province, northern Iran. A triple fecal specimens was collected from each of the 362 participants (183 males, 179 females) residing in six rehabilitation centers of Behshahr, Sari, Amol, Nowshahr and Ramsar. Each specimen was examined by direct wet mounting, formol-ether concentration, Ziehl-Neelsen and trichrome permanent staining. The overall infection rate of intestinal parasite was 26.2% (95 out of 362 subjects; 22.4% in males and 30.2% in females). Giardia lamblia was the most commonly found protozoan parasite (8.0%) followed by Entamoeba coli (5.5%), Blastocystis hominis (3.3%), Endolimax nana (2.8%) and Entamoeba histolytica (1.7%). Double infections were E. coli and B. hominis (1.1%), G. lamblia and Chilomastix mesnili (1.1%), G. lamblia and B. hominis (0.5%), G. lamblia and E. coli (0.5%), E. histolytica and E. coli (0.5%), E. nana and E. coli (0.5%) and E. nana and B. hominis (0.5%). No egg-positive case was found. These helminthic parasites were found to be not common among the participants, 75% of whom had been treated with mebendazole by guardians as a tradition, every 6 months. Nevertheless, our data in rehabilitation centers in northern Iran suggest that infection is not higher than that in community population in recent years in this geographical area.