Although research has demonstrated that marriage education has positive effects on relationship quality, little is known about how such services impact relationships where one partner is incarcerated. The current study implemented an adapted version of the Prevention and Relationship Enhancement Program (PREP Inside and Out) for inmates in Oklahoma correctional facilities. Inmates, with or without their partners, participated in the 12-hour program. The impact of the program was investigated on a range of relationship variables including satisfaction with relationship, dedication, confidence, communication skills, friendship, and negative interactions as reported by the inmate partner. Participants reported substantial gains in all variables and in overall satisfaction with their relationship after completing the program, regardless of their gender and racial/ethnic background. Implications for future marriage education programs and research in prisons are discussed.