Background The course of illness in obsessive-compulsive disorder (OCD) varies significantly between patients. Little is known about factors predicting a chronic course of illness. The aim of this study is to identify factors involved in inducing and in maintaining chronicity in OCD.Methods The present study is embedded within the Netherlands Obsessive Compulsive Disorder Association (NOCDA) study, an ongoing multicenter naturalistic cohort study designed to identify predictors of long-term course and outcome in OCD. For this study, 270 subjects with a current diagnosis of OCD were included. Chronicity status at 2-year follow-up was regressed on a selection of baseline predictors related to OCD, to comorbidity and to stress and support.Results Psychotrauma [odds ratio (OR) 1.98, confidence interval (CI) 1.22-3.22, p = 0.006], recent negative life events (OR 1.42, CI 1.01-2.01, p = 0.043), and presence of a partner (OR 0.28, CI 0.09-0.85, p = 0.025) influenced the risk of becoming chronic. Longer illness duration (OR 1.46, CI 1.08-1.96, p = 0.013) and higher illness severity (OR 1.09, CI 1.03-1.16, p = 0.003) increased the risk of remaining chronic.Conclusions External influences increase the risk of becoming chronic, whereas the factors involved in maintaining chronicity are illness-related. As the latter are potentially difficult to modify, treatment should be devoted to prevent chronicity from occurring in the first place. Therapeutic strategies aimed at alleviating stress and at boosting social support might aid in achieving this goal.