Obesity is an epidemic in this country and much of the rest of the developed world. It is a major contributor to a range of metabolic disorders responsible for much of the medical morbidity and mortality that burden our society. The combination of the costs to society of the chronic illness of schizophrenia with the costs of obesity and the chronic illnesses associated with it, e.g., metabolic disorders, diabetes, dyslipidemias, and cardiovascular disease, represents a major public health problem. Obesity in schizophrenia is accentuated even further largely through illness-related factors, like poor dietary conditions and more sedentary lifestyles, and particularly because many of the psychiatric medications (antipsychotics, mood stabilizers, and antidepressants) used to combat this devastating illness themselves result in weight gain that, if untreated, may result in the usual obesity-associated morbidity and mortality. This article is intended to review some of the physiology of obesity and obesity-related metabolic disorders, the risks to schizophrenia patients engendered by obesity, the evidence for weight gain associated with the antipsychotic drugs, and the possible mechanisms involved in antipsychotic medication-associated weight gain.