The primary goal of this study was to determine whether, rather than how, interactions with cellmates influence the reoffending of prison inmates. More specifically, the study examined whether criminogenic cellmate associations can be causally implicated in the prevalence of the reoffending of the male members of a first-time release cohort from the Pennsylvania Department of Corrections. Both criminological theory and statistical methods inform the analysis. The underlying process being modeled in the current study is a decision. That decision is whether or not two inmates should cell together. Celling decisions might be made by inmates who request cellmates, by correctional officers who assign inmates to cells, or by counselors who recommend inmates for particular prison programs that require particular cell assignments. The study found little support for the hypothesis that social interaction between cellmates can account for the average criminogenic effects of prison peer interaction on reoffending outcomes. The longest-duration cellmate associations maintained by the members of a release cohort from the Pennsylvania Department of Corrections were examined to determine whether the prior criminal experience and criminality of the cellmates would influence the reoffending outcome of the releasees, who spent varying amounts of time with their longest-duration cellmates. On average, no consistent significant associations were found between duration of cellmate association and the releasees' reoffending outcomes. Outcomes included both rearrest and recidivism. On the other hand, there was considerable evidence of marginal prison peer effects; substantial "essential heterogeneity" remained despite the inclusion of numerous statistical controls. 14 tables, 97 figures, extensive references, and appended supplementary information