Aims This study investigates the effect of significant others on treatment outcomes among treated pathological gamblers. Design This is a cohort study of individuals who received gambling treatment. Setting Oregon Problem Gambling Services (OPGS) for gamblers and their family members. Participants 4,410 adult gamblers who were discharged from treatment between August, 2001 and April, 2007. Measurements OPGS enrollment forms provided gambler gender, age, ethnicity, education level, employment status, gambling-related debt, and whether the gambler had a significant other at the time of enrollment. Termination forms provided information on the type of discharge (successful/unsuccessful) and treatment length (in days). Participation of the gambler’s significant other in the family treatment program was identified. Findings Results showed that age, ethnicity, gambling debt, and having a significant other are associated with the odds of successful treatment. Education level moderates the effect of having a significant other on treatment success. Age, ethnicity, education, employment, and having a significant other participate in treatment significantly impacted gamblers’ length in treatment. Conclusions These findings indicate that there may be a benefit to integrating significant others in gambling treatment methods. Significant others may act as social supports for gamblers seeking treatment, and involving loved ones in gambling treatment models may positively affect gambler treatment outcomes.