This report responds to a New York State Legislature request to provide a reliable estimate of the number of persons with developmental disabilities in the state prison system, while evaluating current practices for identifying such inmates and meeting their needs. Major findings included the following: (1) contrary to many estimates, the study found a relatively small proportion (1-3 percent) of prison inmates are developmentally disabled; (2) the battery of academic achievement tests and the Revised Beta Intelligence test administered to all incoming prison inmates appears to be unreliable in identifying developmentally disabled inmates (especially Spanish-speaking inmates); (3) approximately half the inmates with developmental disabilities were identified (largely due to observations) and referred for additional services; (4) the vast majority of inmates with developmental disabilities are "mainstreamed" into the general prison population; and (5) approximately 10 percent of these inmates are housed in two special units for inmates at risk of harm if placed in the general population. The report recommends that resources be directed to integrated programs addressing functional daily living skills, that specialized housing with support services and case management be provided for these inmates when paroled, and that a similar study be conducted of the inmate population of local jails. Appendices provide information scales used, case descriptions of sample inmates, and a bibliography of 41 items. (DB)