The focus of the study was on predicting future criminal careers as a function of prior criminal activity. Arrest data were used as a surrogate for crimes committed. To obtain the number of arrestees, arrest data from Washington, D.C., for 1974-77 was multiplied by the proportion of unique arrests. Results indicate that criminal careers average about 3.3 years (for those starting at 24 years) to 5.6 years (for those starting at 18 years). Property crime careers average 4-5 years, while murder and aggravated assault careers average about 10 years. These findings indicate that for property crimes, including the frequent target offense of robbery and burglary, active offenders in their thirties or early forties are prime targets for sanctioning through incapacitation. Offenders who have persisted in criminal careers to these ages have the longest expected remaining careers. Offenders who have committed murder and rape are still at the peak of their criminal careers in their late twenties and early thirties. Only aggravated assault has passed the bulk of its career by the late twenties. Time served in prison on a sentence averages about 2 years in the United States. Two-year terms represent from one-fifth to one-third of the maximum expected remaining careers for Index offenses combined and for property offenses individually. To the extent that these careers are not merely postponed by incarceration, large portions of those careers can be averted by 2-year prison terms imposed during the period of maximum residual careers. Computations are detailed in the appendixes, and graphic data are provided in the body of the report. Sixty-three references are listed.