The seroprevalence of an anti-Helicobacter pylori antibody (ELISA) was investigated in institutionalized persons with severe motor and intellectual disabilities (SMID). The rate of seropositivity was significantly higher in persons with SMID under 29 years of age than in age-matched controls and in institutionalized patients with muscular dystrophy. No difference in seropositivity among SMID patients was found between those in our and other institutions. Therefore, it is speculated that Helicobacter pylori infection occurs soon after the institutionalization of SMID patients. Persons with SMID living at home, in their teens and twenties, had lower seropositivity than that of institutionalized patients but higher than controls. These data implicate the life style of persons with SMID and long-term institutionalization as one of important risk factors of Helicobacter pylori infection.