The procedure for estimating the number of terms in a prison career proceeds in two stages: estimates of probabilities of recidivism and estimates of the distributions of the numbers of prison terms. The data consists of an entire population of 16,433 prisoners released for the first time between 1975 and 1987 from Western Australian prisons. Results indicate that only a small number of prisoners acquire large numbers of terms and, consequently, account for a high proportion of all imprisonment. This group represents a core of high-risk recidivists that has long attracted the interest of those who give high priority to preventive goals. Recent work on seriousness and progression also supports the view that those who have long careers tend to progress to more serious offending. 4 tables, 2 figures, and 30 references (Author abstract modified)