Objective: To examine the predictive role of insomnia andsleep duration on the 2-year course of depressive andanxiety disorders. Method: This study is a secondary data analysis based ondata from the baseline (2004-2007) and 2-year assessmentof the Netherlands Study of Depression and Anxiety.Participants were 1,069 individuals with DSM-IV-baseddepressive and/or anxiety disorders at baseline. Sleepmeasures included insomnia (Women's Health InitiativeInsomnia Rating Scale score ≥ 9) and sleep duration(categorized as short [≤ 6 hours], normal [7-9 hours], orlong [≥ 10 hours]). Outcome measures were persistence of DSM-IV depressive and anxiety disorders (currentdiagnosis at 2-year follow-up), time to remission, andclinical course trajectory of symptoms (early sustainedremission, late remission/recurrence, and chroniccourse). Logistic regression analyses were adjusted forsociodemographic characteristics and chronic medicaldisorders, psychotropic medications, and severity ofdepressive and anxiety symptoms. Results: The effect of insomnia on persistence of depressiveand/or anxiety disorders (OR = 1.50; 95% CI, 1.16-1.94)was explained by severity of baseline depressive/anxietysymptoms (adjusted OR with severity = 1.04; 95% CI,0.79-1.37). Long sleep duration was independentlyassociated with persistence of depression/anxiety evenafter adjusting for severity of psychiatric symptoms(OR = 2.52; 95% CI, 1.27-4.99). For short sleep duration, theindependent association with persistence of combineddepression/anxiety showed a trend toward significance(OR = 1.32; 95% CI, 0.98-1.78), and a significant associationfor the persistence of depressive disorders (OR = 1.49; 95%CI, 1.11-2.00). Both short and long sleep duration wereindependently associated with a chronic course trajectory(short sleep: OR = 1.50; 95% CI, 1.04-2.16; long sleep:OR = 2.91, 95% CI, 1.22-6.93). Discussion: Both short and long sleep duration-but not insomnia-are important predictors of a chronic course, independent of symptom severity. It is to be determined whether treating these sleep conditions results in more favorable outcomes of depression and anxiety. © Copyright 2013 Physicians Postgraduate Press, Inc.