The prevalence of overweight and obesity in untreated patients with severe mental illness mimicks the trends seen in the general population. Furthermore, weight gain is likely to occur with the addition of pharmacotherapy with an antipsychotic. The literature does indicate that despite fundamental cognitive and psychosocial deficits seen in patients with severe and persistent mental disorders such as schizophrenia and bipolar disorder, it is possible to effectively manage weight gain in this population. In particular, behavioral interventions have been shown to be effective in the prevention and treatment of weight gain associated with antipsychotic therapy. Some success has also been seen with the use of adjunctive medication such as amantadine, histamine (H2) antagonists, metformin, topiramate, and orlistat. Additional, prospective, controlled studies of long-term antipsychotic drug associated weight gain and its clinical consequences are needed in order to identify the most effective therapy for the reduction and maintenance of body weight in patients taking antipsychotic therapy.