A previously unrecognized mental retardation malformation syndrome was observed in five unrelated Japanese children. Consistent clinical features included moderate-to-severe mental retardation, progressive dwarfism of postnatal onset, a peculiar facies characterized by long palpebral fissures, with eversion of the lateral third of the lower eyelids, arched eyebrows, broad and depressed nasal tip, large prominent earlobes, short fifth fingers, abnormal dermatoglyphics including absence of digital triradius c or d, and frequent otitis media in infancy. Inconsistent abnormalities included epicanthal folds, cleft or high-arched palate, widely spaced teeth, low occipital hair line, scoliosis, and dislocation of the hip joint. Neither familial occurrence nor parental consanguinity was noted. The etiology of the malformation syndrome remains unknown.