The objective of this study was to compare in a single blind manner, over a period of 12 weeks, the efficacy and tolerability of two different titration regimens of sertraline in the treatment of OCD: 150 mg/day reached at day five from the beginning of therapy (rapid titration regimen) versus 150 mg/day reached at day 15 from the beginning (slow titration regimen). Patients with a DSM-IV diagnosis of OCD and a Y-BOCS greater or equal to 16 were randomly assigned to receive one of the two dosing regimens; an upper target dose of 150 mg/day was selected on the basis of a review of mean dosages used in flexible-dose sertraline studies. The primary efficacy measure was the Y-BOCS, which was completed at baseline and every 2 weeks. Thirty-two patients referred to the Anxiety and Mood Disorders Unit of the University of Turin were included in the study. Seventeen were assigned to the rapidly escalating dose regimen and 15 to the other titration regimen. Twenty-seven (84.4%) patients completed the 12 weeks of the study: 14 (82.4%) patients in the rapid and 13 (86.7%) in the slow titration regimen. The ANOVA analysis showed a significant difference between treatment groups at week 4 and 6 in favor of the rapid titration regimen group; this difference faded afterwards. Both titration regimens were effective in reducing OC symptoms and were well tolerated: no differences in drop-out or in adverse event rates emerged between the two groups. Limitations of the present study are the single-blind design and the lack of power to detect differences in tolerability.