This article presents a systematic, retrospective case-note survey of a specialist obsessive-compulsive disorder (OCD) outpatient service. We explore the frequency of 'high-dose' selective serotonin reuptake inhibitor (SSRI) prescribing and describe clinical outcomes in a naturalistic clinical setting. Patients receiving high doses were compared with 'control' cases at the following three time-points: referral, initiation of high-dose SSRI and last clinical assessment.Twenty-six (13.5%) out of 192 patients received high-dose treatment for 3-364 weeks (mean 81.5 weeks; SD = ±95.1). At referral, high-dose patients were significantly more likely than controls to be male, and to have received Cognitive Behavioural Therapy (CBT), although illness severity and complexity did not differ. At initiation of dose escalation, however, high-dose patients were significantly more symptomatic than controls (Yale-Brown Obsessive Compulsive Scale score [Y-BOCS 25.4 vs. 17.7]). At the last assessment, patients on high-dose treatment showed significant within-group improvements (Y-BOCS 25.35 vs. 20.95), although endpoint scores for the high-dose group remained significantly higher than control patients treated for a matched period (Y-BOCS 21.0 vs. 15.5), suggesting enduring treatment-resistance. Frequency of adverse effects did not significantly differ between the two groups. Our results suggest that high-dose SSRI was associated with clinical improvement and well-tolerated in a particularly refractory OCD sample.