INTRODUCTION: A clinically useful diagnostic classification should identify most patients who are treated. To our surprise, DSM-IV criteria for major depressive episodes (MDE) detected fewer than 50% of a community sample (the Zurich study) who had received treatment for depression.1 Treated subjects often experience episodes lasting under 2 weeks, or with fewer symptoms than required for a DSM diagnosis. METHODS: Our paper focuses on the validity and clinical relevance of the length of depressive syndromes, defined by the presence of 5 or more of 9 diagnostic symptoms (DSM-IV). RESULTS: We found depressive syndromes lasting under 2 weeks to be highly prevalent, and those lasting 4+ days to have equal validity (family history, age of onset, course) and treatment rates to episodes of 2-4 weeks. CONCLUSIONS: The 2-week criterion for MDE would appear questionable. Our results need confirmation by larger epidemiological studies.