Research on alcohol and substance use in First Nations populations frequently describes the nature of the problem, and the severity of the risk factors, but seldom addresses possible interventions and the effectiveness of the treatments that clients do engage in. This paper reviews a participatory evaluation of the 6-week residential "Namgis Treatment Centre" (NTC) program in Alert Bay, British Columbia. Intake files (n = 218) were reviewed for clients who participated in 17 different 6-week sessions over a period of two and a half years. The assessment included a telephone follow-up survey, developed in conjunction with all of the NTC staff, for clients who had been out of treatment for 3-37 months (n = 91, 52.7% male and 47.3% female participants). In total, 24 clients (26.37%) were abstinent at the time of the interview, and 67 clients (73.6%) had had a relapse on average 155.29 (SD = 167.77) days after completing treatment. Cox regression univariate and bivariate analysis revealed that pre-treatment variables were not associated with time to relapse or what happened after relapse (abstinence again, harm reduction or resuming pre-treatment consumption levels). However, the greater number of supports the client had, the more likely they were to be completely abstinent, and the less supports the client had, the more likely they were to completely relapse. NTC staff and community members were consulted on the implications of the data, and recommendations were shared with NTC policy makers. Based on the findings of this project, it is apparent, that in this context, follow-up and aftercare are critical for effective treatment.