Since Magnus Huss introduced the diagnosis of 'chronic alcoholism' into medical literature in 1849, two unsolved problems concerning classification have remained: (1) Differentiation between problem drinkers and chronic alcoholics fluctuates, whereby the cut point of differentiation between abuse and addiction remains differently defined by different authors. Some authors view alcohol-induced damage as a building-stone of diagnosis of chronic alcoholism whereas other authors define these damages as illnesses developed as a consequence of chronic alcohol intake. This fact is also mirrored in the different definitions of chronic alcoholism by different classification systems, like ICD-9, DMS-III or DMS-III-R. Valid and reliable questionnaires, like the Munich Alcoholism Test or the Problem Drinking Scale did not succeed in solving this problem of definition, either. (2) The fact that chronic alcoholics are sick--in the sense of a biological-medical approach--is undoubted. Our research group was able to prove that chronic alcoholic patients metabolize methanol in a different way from that of healthy persons. The biological, sociological and psychopathological heterogeneity of this illness has been stressed for more than a century. A prospective long-term study carried out over 4-7 years has led to the development of a new typology in chronic alcoholism that is able to differentiate subgroups of chronic alcoholic patients cross-sectionally in a clinical, biochemical and neurophysiological way. Diagnosis according to this typology qualitatively differentiates patients in many spheres other than drinking behavior. These subgroups also require correspondingly modified therapeutic strategies.