Monthly reports that presented end-of-the-month number counts for each of the major study variables during a period of sharp increase in inmate population from January 1972 to December 1975 were collected on youthful offenders, adult male offenders, older age male offenders, and female offenders in four Florida prisons. The independent variable was prison population size and the dependent variables which were indicators of behavior changes included number of escapes, number of inmates confined in disciplinary confinement, number of assaults on employees, number of assaults on inmates, and number of inmates enrolled in classes of grades 1 through 12. When population size was correlated with each individual behavior change indicator of the four institutions together, a positive relationship was found with all the behavior change indicators except four: escape, high school equivalency exam, vocational education certificates issued, and parole. This indicated that when the population size increased, incidents of most of the disruptive and constructive behavior increased at a faster rate than the increase in institutional population. When each institution was examined separately, overcrowding was positively related to disruptive behavior, although the strength of this relationship varied with different types of institutions. Additional findings were that overcrowding and constructive behavior were negatively related, and the strength of this correlation also varied with different types of institutions. However, it was found that, except at youthful offender and older age offender prisons, the rate of disruptive behavior changes, with the exception of assault, were not significantly related or negatively related to the overcrowding index. The possibility of uneven distribution of inmates within the prisons studied is noted as a possible study limitation. A summary table of study findings and six references are provided.