An association between psychiatric disorders in childhood and the later development of major depressive disorders (MDD) has been suggested. However, no prospective population-based cohort study has been able to directly compare the risks of MDD following a broad spectrum of child and adolescent psychiatric disorders.

To use a large, register-based cohort to establish whether or not psychiatric disorders in childhood lead to a higher risk of later MDD and, if so, which disorders are associated with the highest risks.

To estimate and compare the risk of later MDD in children diagnosed with one of ten psychiatric disorders

Using Danish population-based registers all persons born in Denmark from 1990 through 2000 were identified and followed from their 5^th birthday through 2012. Cumulative incidences and incidence rate ratios of MDD following each of ten exposure disorders were calculated

We followed 960,026 persons, contributing 8,778,331 person-years. Among these 7,787 were diagnosed with MDD (incidence=1.7/1000 pyrs).

Diagnosis of any psychiatric disorder led to an absolute risk of MDD within eight years of 1.6% in males and 4.98% in females with early onset (ages 0-14) and 7.02% in males and 15.98% in females with late onset (ages 14-18).

For all groups, anxiety and eating disorders were associated with the highest risks of MDD.

Most disorders were associated with a significantly increased risk of later MDD and children with anxiety and eating disorders carry the greater risk. Future research should focus on common pathways between depression and other psychiatric disorders.