Developmental data from 612 patients with Down's syndrome have been collected over a period of 20 years from an outpatient clinic for mentally retarded children. Ss' ages ranged from birth through 16 years, all being reared in their homes. With higher percentages of children with Down's syndrome remaining in the home environment and eventually attending day care programs, questions naturally arise concerning the developmental expectations of such children. To answer some of these questions developmental information was abstracted from the clinical records and subjected to statistical analysis. These data include motor and language development and intellectual growth. Despite the limited sample developmental norms for children with Down's syndrome were established, which should prove useful in clinical evaluation.