This second German study of the effectiveness of social therapy in prison based on an experimental design sought to answer three questions: (1) What is the extent of success of social therapy in an experimental investigation? (2) Is it possible to estimate the success of social therapy in prison in a theoretical ideal case? and (3) Is the influence of incarceration as an unfavorable socialization process lower, equally effective, or more effective than the favorable influence of social-therapeutic programs administered during the course of imprisonment? At the time of the random assignment, there were 228 random respondents: 114 belonged to the experimental group, and 114 were in the control group. The official recidivism as recorded by the Federal Central Register as the main criterion of the study was available for 223 of all 228 respondents. Of random respondents, 225 participated in the first sweep (outset of social therapy), 217 in the second sweep (1 year after social therapy), 190 in the third sweep (shortly before release), and 150 in the fourth sweep (2 years after release). Findings show that the success of social therapy in prisons is low to very low in a randomized study. The relatively low success of social therapy cannot be explained by a lack of effort by the social therapists. Overall, the study shows that prison is not a favorable setting for achieving positive behavioral changes in offenders. 8 tables, 6 notes, and 18 references