In the first period of the study (1967 to 1975) the prison population diminished as the result of changes in law. In the second phase (1975, the prison population grew, reaching the highest level in thirty years (35,655 prisoners) in 1980; the average annual increase for the period was 6.5 percent. The male population makes up more than 96 percent of the prison population, and has developed along the same lines as the overall prison population. The number of females dropped more rapidly than that of males until 1976, then grew more rapidly than the male prison population until 1980. The prison population consists of both accused and convicted offenders. The reduction/growth patterns of both groups resemble those of the overall prison population, although variations in the number of convicted offenders are greater than variations for accused offenders. In the period 1967 to 1980 the proportion of French prisoners has remained greater than 80 percent, although the foreign prison population has risen gradually from 15 percent in 1967-1974 to 20 percent in 1980. Statistics on the male metropolitan prison population indicate that prison admissions are highest in the first quarter of each year and lowest in the third quarter, and that releases are lowest in the third quarter and highest in the fourth quarter. More than 58 percent of the prisoners are individuals whose investigation is not yet complete and who have been detained for less than 8 months. The proportion of the prison population serving very long sentences has remained relatively stable (10 percent in 1980). The number of long sentences has increased to 24.9 percent in 1980, while the number of short and moderate sentences has decreased to around 64 percent in 1980. In 1980, more than 50 percent of the prison population was serving sentences for theft. From 1976 on the number of sentences for every category except simple theft has increased at a regular rate. From 1968 to 1977 the average age of prisoners dropped from 31.9 to 29.8 because of increases in the 21-to-25 year old group and the 25-to-30 age group. After 1977 the average age rose again slightly. Various projections of the prison population in 1981 and 1982 are outlined. Tables and notes are provided.