Some 211 male alcoholic in-patients were compared with a simple random sample of 200 men from Greater Stockholm. The group of male alcoholic in-patients and the random sample were subdivided with respect to alcohol consumption and use of hepatotoxic drugs: (IA) men from the random sample with low or moderate alcohol consumption and no use of drugs (n = 169); (IB) men from the random sample with low or moderate alcohol consumption with use of drugs (n = 31); (IIA) alcoholic in-patients with use of alcohol but no drugs (n = 171); (IIB) alcoholic in-patients with use of alcohol and drugs (n = 40). Earlier and more severe alcohol-related and anti-social problems were found among subjects with an alcoholic parent than among subjects without an alcoholic parent. The highest level of problems was noted for subjects with alcoholism in both parents and among the alcoholic in-patients. Groups which resembled each other were the drug users in the alcoholic group and in the general sample. Both inherited and environmental factors are important determinants and many of these individuals have psycho-social problems as children and adults. The children of those adults who used alcohol in combination with drugs (IIB) had most problems and the most severe problems. In the general population sample, those who used alcohol in combination with drugs (IB) had so many problems in the family and psycho-social problems themselves that they resembled the alcoholic in-patients and especially the group with high alcohol consumption in combination with drugs (IIB). A new finding is that the high-risk groups IB and IIB, who used both alcohol and drugs, had experienced a more disturbed school career and were more aggressive, had more nervous problems, and were more emotionally disturbed than the other groups. It is concluded that alcohol and drug use by parents may be predictive of future alcoholism in their children.