The prevalence of the metabolic syndrome and its sequelae (cardiovascular diseases and diabetes mellitus) is elevated in patients with depression and schizophrenic disorders in comparison with mentally healthy persons. A variety of factors have been proposed to explain this association. These include overlapping pathophysiological mechanisms, an unhealthy lifestyle (poor dietary choices, smoking, lack of exercise), genetic factors and a lack of compliance with therapeutic programs. In addition to this, attention is increasing being focused on the metabolic side effects of (atypical) neuroleptics. Cases of acute ketoacidosis may also be associated with the use of these substances. Since none of the neuroleptics currently commercially available can be guaranteed to be free of metabolic side effects, strict monitoring of depressive or schizophrenic patients receiving such treatment is mandatory.