Association studies have been proposed to identify the genetic determinants of complex neuropsychiatric traits. Although such studies of candidate genes offer great potential to identify genetic variants that contribute to the expression of psychiatric disease, no consistent associations have been identified. Studies to date have focused on candidate genes that are selected for analysis on the basis of incomplete information about gene function in the brain, therefore the majority of genes expressed in the brain have been ignored. Additionally, most genetic determinants of psychiatric disease will probably be of modest effect and therefore require association studies of large samples. As genomic technologies advance, massive genotyping of large samples should allow identification of alleles that contribute to psychopathology.