We revise the articles dealing with psychiatric comorbidity of alcohol dependence. This study focuses on the epidemiology and on the etiopathogenic involvement. The epidemiologic studies in community samples show that psychiatric comorbidity in alcohol dependence is twice as big as expected and this excess is common in every psychiatric disorder. However, this excess is bigger in antisocial personality, other substance-related disorders and in schizophrenia. This excess of comorbidity can be due to two factors: how alcohol can cause psychiatric disorders, and how psychiatric symptoms can produce an increases of alcohol consumption which can lead to dependence in people with vulnerability.