The prevalence of the metabolic syndrome is increased 2—3-fold among people with severe mental illness (SMI) and may explain the high risk of cardiovascular disease in this patient group. The reason for the increase in the metabolic syndrome in people with SMI is unclear but is likely to be multifactorial, including both hereditary and environmental factors. There are concerns that antipsychotic medication may be responsible for the increased prevalence of diabetes, the metabolic syndrome and cardiovascular disease in people with SMI. While the evidence linking the antipsychotics with diabetes remains inconclusive, certain antipsychotics, notably olanzapine and clozapine are associated with weight gain and hypertriglyceridaemia. At present there is little systematic monitoring of cardiovascular risk factors in people with SMI and consequently there is a high prevalence of undiagnosed metabolic problems. The burden of cardiovascular disease and diabetes could be reduced in people with SMI if lifestyle intervention was instituted and pharmacotherapy used when indicated. The adverse effects of antipsychotic medication should be balanced with the therapeutic benefits which may be important in ensuring that patients are able to make the necessary changes to reduce the burden of diabetes and cardiovascular disease.