The original study was completed in 1996 and did not employ multivariate methods or survival analysis to study treatment retention. By re-analyzing these data in 2001, information was derived on the types of clients that succeed in jail-based substance user treatment interventions and the types of programs that foster success. Success was measured by treatment retention or the number of calendar days in treatment. In this study, three events determined when the length of time in treatment ceased: (1) dropping out of treatment, (2) completing treatment, and (3) being released from or transferred out of jail before either other event occurred. The study population examined included inmates that were voluntarily admitted to jail-based treatment for substance use disorders. The results indicate that older inmates (over 25 years of age) were significantly more likely to remain in jail-based substance user treatment longer than were younger inmates, a finding that is consistent with existing literature. Inmates that reported using methadone at jail admission were significantly more likely to leave treatment early than were inmates that did not report using methadone. Inmates that had not been sentenced were significantly more likely than were sentenced inmates to leave treatment early. The Substance Abuse Intervention Division (SAID) and Deciding, Educating, Understanding, Counseling, and Evaluation (DEUCE) programs were significantly more effective at retaining inmates than were the other programs. The SAID program was a modified therapeutic community, and the DEUCE program was a curriculum-based intervention. The policy implications of this research indicate that certain types of inmates are probably more receptive than others to jail-based treatment for substance use disorders. More research is needed to determine what types of programs produce the best outcomes. 1 figure, 3 tables, 52 references