Under Pennsylvania's mandatory sentence statutes, the defendant does not have to be notified that the State intends to seek a mandatory sentence for an offense until after conviction. Pennsylvania sentencing law mandates a 5-year minimum sentence for crimes involving a firearm and also establishes minimum criminal penalties for driving under the influence. The legislature has also enacted mandatory minimum sentences for drug convictions that set a sentence range of 1 to 8 years. Mandatory sentencing has affected prison overcrowding, and length of individual sentences is a key factor. While the average minimum prison sentence in 1992 was 30.4 months, the average mandatory minimum sentence was 50.4 months. In addition, because mandatory sentence length is often 1 year or more, offenders are subject to a place of confinement under Pennsylvania's Rules of Criminal Proceedings. This statute specifies that inmates serving a maximum sentence of 5 years or more must serve their sentence in a State institution. The cumulative effect of sentences that mandate a minimum sentence of 1 year or more has been an increase in the number of offenders serving sentences in State correctional facilities. Changing characteristics of the State prison population are examined, as well as disparity in the racial distribution of mandatory sentences, and the deterrent value of mandatory sentences is discussed. 6 references, 2 tables, and 3 figures