This study investigated the relationship between weight loss, locus of control, and social support. It was hypothesized that internals would be more successful in weight reduction than externals/powerful others or externals/chance; that participants with higher social support scores would be more successful in weight reduction than participants with lower social support scores; and that social support would contribute more to success in weight reduction in externals/powerful others than in internals or externals/chance. Subjects were 46 female employees of a large life insurance company who had participated in a nutrition and weight control program. They were studied six months later to assess weight change, locus of control (specifically, using a multidimensional health locus of control scale and a modified weight locus of control scale) and social support (using an investigator-developed scale). Study findings did not support the hypotheses. Rather, a significant negative relationship was found between social support and weight reduction in the case of internals. Possible explanations for the findings were discussed, along with recommendations for practice and further research. For example, it was suggested that it may be most desirable for those attempting weight loss to be sufficiently internal that they believe they are capable of bringing their weight under control, yet sufficiently external that they are amenable to the advice of health professionals.