In our study, 40 adult outpatients with OCD, who have been insufficiently responsive to at least two recognized drug treatments, will be randomly assigned to one of two treatment groups (active low frequency (1 Hz, 100% of the motor threshold) rTMS or sham-placebo) applied to the SMA daily for up to four weeks. An individual MRI-guided neuronavigation will be used to precisely define the target stimulation site in each patient. Rating scales for symptom change will be obtained at baseline, during the rTMS course, at the end of 4 weeks of treatment, and after a 2-month follow-up period. The main outcome measure will be the Yale-Brown Obsessive Compulsive scale, and secondary outcome measure will include the CGI scales, the LPO scale, the MOCI, and the SDS. Brain activity changes in fMRI before and after active/sham treatment will be compared between groups, with rest measures and provocation tasks.