Genetic epidemiological studies suggest that individual variation in susceptibility to schizophrenia is largely genetic, reflecting alleles of moderate to small effect in multiple genes. Molecular genetic studies have identified several potential regions of linkage and two associated chromosomal abnormalities, and evidence is accumulating in favour of several positional candidate genes. Currently, the positional candidate genes for which we consider the evidence to be strong are those encoding dysbindin (DTNBP1) and neuregulin 1 (NRG1). For other genes, disrupted in schizophrenia 1 (DISC1), D-amino-acid oxidase (DAO), D-amino-acid oxidase activator (DAOA, formerly known as G72) and regulator of G-protein signalling 4 (RGS4), the data are promising but not yet compelling. The identification of these, and other susceptibility genes, will open up new avenues for research aimed at understanding the pathogenesis of schizophrenia, and will catalyse a re-appraisal of the classification of psychiatric disorders.