For the past 30 years, overweight and obesity has increased at alarming rates in the general population. This public health crisis has affected persons with mental illnesses as it has those in the general population. Little is known about how individuals with psychiatric problems respond to weight-loss treatment compared to the general population. The current study examines the efficacy of a cognitive-behavioral group weight-loss intervention with such individuals. The study also examines self-esteem, motivation, and the involvement of a support person in treatment as predictor variables. The treatment was shown to be effective regardless of depression severity. However, while all participants with a support person completed the intervention, those without support were more likely to drop out. Participants also reported improvements in self esteem after treatment completion. Keywords: overweight, obesity, weight-loss, mental illness, depression, self-estee