The current study investigates informal social structure among prison inmates. Data come from the Prison Inmate Network Study (PINS), a project focused on a unit of a Pennsylvania medium security men’s prison. We focus on 205 inmates and their “get along with” network – an approximation of friendship in other settings. We find a weak subgroup structure dominated by two groups of “old heads” and characterized by moderate (non gang-based) race/ethnic clustering. Structurally, the network resembles adolescents in schools, suggesting that prison inmates are capable of successfully building peer associations. We conclude that under the right conditions self-organizing inmate society can foster social integration reminiscent of other social settings.