This study explored the efficacy and tolerability of very high doses (maximum dose of >40 mg/day), high doses (maximum dose of 25–40 mg/day), and standard doses (maximum dose of ≤20 mg/day) of escitalopram (ESC) as an anti-obsessive–compulsive disorder treatment in a naturalistic clinical setting. We reviewed the medical records of all patients with obsessive–compulsive disorder (n=246) who had taken ESC between May 2006 and September 2009, and assigned Clinical Global Impression (CGI) scores, retrospectively. Of the total sample, 24.4, 38.2, and 37.4% patients received very high, high, and standard doses of ESC, and the mean daily maximum doses of ESC were 57.3±12.0 mg, 33.9±5.4 mg, and 13.4±5.8 mg, respectively. The CGI-Severity scores in each group decreased significantly after treatment with ESC, as evidenced by response rates (i.e. CGI-Improvement scores of 1 or 2) of 46.3, 43.2, and 26.2%, respectively. Although some adverse events increased in a dose-dependent manner, most could be managed with an ESC dose adjustment. These results imply that doses less than or equal to 40 mg/day ESC are sufficient for symptomatic improvement with good tolerability for most patients. Very high doses of ESC, on the other hand, can be considered for patients with inadequate therapeutic responses to the administration of 40 mg/day ESC.