ABSTRACT: OBJECTIVE: To validate the ICD-10 diagnosis of a single depressive episode as used in daily clinical psychiatric practice and as recorded in the Danish Psychiatric Central Research Register. METHODS: Patients discharged with a diagnosis of a single depressive episode were consecutively sampled from the register and diagnosed according to an interview using the Schedules for Clinical Assessment in Neuropsychiatry (SCAN). RESULTS: A total of 75.4% of 399 patients with a register diagnosis of a single depressive episode also got this diagnosis according to the SCAN interview (82.8% for severe type of a single depression, 76.0% for moderate type of a single depression and 65.2% for mild type of a single depression). CONCLUSION: The ICD-10 diagnosis of a single depressive episode can be used in daily clinical practice with sufficient precision. The validity of the diagnosis is highest for severe and moderate type of depression and decreases for mild depression.