Given the spectacular advances of genetics during the last five years, it seems appropriate to revisit the important subject of genetics of alcoholism and substance abuse. In recent studies alcohol abuse was shown to have an heredability of roughly 38%, whereas psychostimulant and opiate use exhibit heredabilities of 11 to 45%. The heredability of smoking was found to be around 50%. There is a strong comorbidity between alcoholism and smoking. More than 80% of alcoholics smoke cigarettes in the U.S.A.. Other genetic methods such as linkage analysis, allele sharing methods, association studies and analysis of inbred, transgenic and gene-knockout rodents, have partially agreed in showing that the 5HT-IB serotonin receptor and the DRDI, DRD2 and DRD4 dopamine receptors, as well as the dopamine transporter DAT, play an important role in behaviors related to alcoholism and substance abuse. Some neurochemical markers, as for example monoamine oxidase and adenylate cyclase have also been implicated in addictive disorders. The aldehyde dehydrogenase allele ALDH2*2 has a protective effect against alcoholism. Two whole genome linkage studies have shown linkage to chromosomal regions that are in the proximity of the DRD4 dopamine receptor, the GABA receptor gene cluster and the alcohol dehydrogenase gene cluster (Rev Méd Chile 2000; 128: 1279-82)