The relatively high comorbidity of type 2 diabetes and schizophrenia may suggest a shared biological susceptibility to these two conditions. Family studies have demonstrated an increased risk of diabetes in unaffected relatives of patients with schizophrenia, consistent with a heritable susceptibility trait. Linkage analyses have identified several loci that are associated with schizophrenia and some of these, notably those on chromosomes 2p22.1-p13.2 and 6g21-824.1 have also been observed in linkage studies in type 2 diabetes. In addition, the dopamine D5 receptor on chromosome 5 and the tyrosine hydroxylase gene on chromosome 11 have both been suggested as candidate genes in schizophrenia and may also be implicated in susceptibility to poor glycaemic control. In addition, an increased rate of type II diabetes has been observed in some patients treated with antipsychotics. Potential neurochemical substrates of this effect include the histamine H1 receptor, the 5-HT2C serotonin receptor or the beta3 adrenoreceptor. However, the search for a genetic basis to the association between diabetes and schizophrenia is still in its infancy, and much further work needs to be performed, including the systematic screening of all confirmed susceptibility loci and quantitative trait locus mapping of glycaemic control.