In States for which the National Council on Crime and Delinquency (NCCD) developed prison population projections in 1990, the number of drug offenders admitted to prison increased by 96 percent between 1988 and 1990, while the total number of prison admissions increased by 38 percent. Due primarily to changes in law enforcement practices, prison and jail crowding, aging of the baby boom population, and fiscal constraints of State and local governments, the growth in prison admissions began to slow by 1991. In 1991, total prison admissions in the 16 States grew by less than 3 percent and drug admissions actually declined by an average of 10 percent. In marked contrast to prison admission trends, prison populations grew by 38 percent between 1990 and 1994. In States with indeterminate sentencing, daily prison populations increased at a rate far greater than new court commitments to prison. This resulted from changes in sentencing and parole board policies that mandated longer lengths of stay and an increased number of parole revocations. Legislative changes designed to abolish parole, enhance mandatory minimum sentences, and implement various truth-in-sentencing measures will increase lengths of stay for selected inmates. According to the NCCD, these changes will increase prison populations by 19 percent between 1995 and 2000. The NCCD projects that the U.S. prison population will reach 1.4 million inmates by the year 2000. 11 references, 3 notes, 4 tables, and 2 figures