The role of comorbidity as a risk for suicide attempts is investigated in a random sample of 3021 young adults aged 14-24 years. The M-CIDI, a fully standardized and modified version of the Composite International Diagnostic Interview, was used for the assessment of various DSM-IV lifetime and 12-month diagnoses as well as suicidal ideation and suicide attempts. Of all suicide attempters, 91% had at least one mental disorder, 79% were comorbid or multimorbid respectively and 45% had four or more diagnoses (only 5% in the total sample reached such high levels of comorbidity). Suicide attempters with more than three diagnoses were 18 times more likely (OR = 18.4) to attempt suicide than subjects with no diagnosis. Regarding specific diagnoses, multivariate comorbidity analyses indicated the highest risk for suicide attempt in those suffering from anxiety disorder (OR = 4.3), particularly posttraumatic stress disorder followed by substance disorder (OR = 2.2) and depressive disorder (OR = 2.1). Comorbidity, especially when anxiety disorders are involved, increases the risk for suicide attempts considerably more than any other individual DSM-IV diagnoses.