The present paper reports lifetime prevalence rates of mental disorders in the 18- to 64-year-old general population of a northern German region. A representative random sample from registration office files of 4,075 individuals was examined in personal interviews using the fully standardized and computerised "Munich Composite International Diagnostic Interview" (M-CIDI). The response rate was 70.2%. Individuals were classified according to the DSM-IV. Substance use disorders were most frequent with 25.8% followed by anxiety (15.1%), somatoform (12.9%), affective (12.3%), and eating disorders (0.7%). Disorders other than substance use were more frequent in women and less frequent in men. A trend toward less psychiatric morbidity exists in individuals with higher educational level, higher income, and those who are married or reside in rural communities. Of all individuals affected by mental disorders, 42% fulfilled the criteria for at least one additional disorder. The results are discussed against the background of selected previous studies.