Weight gain is a serious adverse event during neuroleptic or antipsychotic treatment of schizophrenic disorders. The risk of weight gain varies among the class of neuroleptics, however no reliable predictors exist that adequately estimate individual risk. It is hoped that molecular genetic tests will help determine individual risk in the future. This article summarizes studies performed till now and concludes that gene variants of the serotonin 2C receptor and leptin significantly correlated with weight gain in several studies. Further interesting findings were obtained with variants of CYP2D6, the synaptosome-associated protein of 25 kDa (SNAP-25) as well as with the adrenergic alpha-2A genes. The group sizes were however small, and more studies are required for genetic tests to become available. Nonetheless the first steps towards genetic risk assessment have been performed, and its application in the near future has become likely.