Three unrelated Puerto Rican boys, ranging in age from 3 to 4 years, had marked, central, non-progressive hypotonia, chronic constipation, severe psychomotor retardation, seizures or abnormal electroencephalograph or both, abnormal dermatoglyphics, delayed bone age, dysharmonic skeletal maturation, and preponderance and larger size of type 2 muscle fibres. Additional findings included narrow, high arched palate, prominent nasal root, long philtrum, distended abdomen, and drooling from open mouth. Two of the three patients also had undescended testes, hypertelorism, and tapered fingers. Birth weight, postnatal physical growth, and head size were average. Family and gestational histories and laboratory evaluations were normal. The combination of features observed in the three boys appears to be distinct and to represent a new syndrome.