Characteristics of the older developmentally disabled adult were studied in an examination of data collected on 485 randomly selected clients in four age categories; 18 and under (N=74), 19-54 (N=336), 55-64 (N=48), and 65 and over (N=27). Medical and physical problems were assessed, including general health, mobility problems, and prescription of medications. Among clients ages 65 and over, 50% were classified as having a life-threatening physical condition, compared to 11% of clients aged 55-65 and 6% of those under 54. The highest percentage of mobility problems occurred in the under-18 and over-65 age groups. Antipsychotic drugs were prescribed for 54% of clients over age 65. After age 65, decided decrements were observed in independent functioning, physical development, self-direction, and socialization. Clients in this age group also lived in the most restricted residential environments. Significant increases were noted in the upper two age groups in self-abusive behaviors and hyperactive tendencies, as measured by Part II of the Adaptive Behavior Scale. Additional results are presented, and the interpretation and implications of data are discussed in terms of programming for older developmentally disabled adults. References and tables are appended. (JW)