Objective: Psychiatric comorbidities are common among psychiatric patients and typically associated with poorer clinical prognoses. Subjects of a large Danish birth cohort were used to study the relation between mortality and co-occurring psychiatric diagnoses. Method: We searched the Danish Central Psychiatric Research Registry for 8109 birth cohort members aged 45 years. Lifetime psychiatric diagnoses (International Classification of Diseases, Revision 10, group F codes, Mental and Behavioural Disorders, and one Z code) for identified subjects were organized into 14 mutually exclusive diagnostic categories. Mortality rates were examined as a function of number and type of co-occurring diagnoses. Results: Psychiatric outcomes for 1247 subjects were associated with 157 deaths. Early mortality risk in psychiatric patients correlated with the number of diagnostic categories (Wald ײ = 25.0, dl = 1, P < 0.001). This global relation was true for anxiety and personality disorders, but not for schizophrenia and substance abuse, which had intrinsically high mortality rates with no comorbidities. Conclusions: Risk of early mortality among psychiatric patients appears to be a function of both the number and the type of psychiatric diagnoses.