To be included in the study all the patients must be aged between 18 and 65 yy and have to meet DSM-5 criteria for OCD with a Y-BOCS total score > or = 20 and a history of treatment-resistant OCD, established by a trained psychiatrist with extensive expertise in the OCD field. Treatment-resistance is defined as non-response (less than 25% reduction of the Y-BOCS score) after at least one SRIs trials (clomipramine, fluoxetine, sertraline, paroxetine, fluvoxamine, citalopram, escitalopram) at the maximum tolerable dose for at least 12 weeks. Potential patients with any of the following conditions will be excluded: 1) any additional current psychiatric comorbidity, except for mild depressive and anxious symptoms or tics; 2) a lifetime DSM-5 diagnosis of schizophrenia or other psychotic syndromes, substance dependence or substance abuse, including alcohol, bipolar I or II disorder, mental disorder due to a general medical condition; 3) serious suicide risk; 4) episodic OCD; 5) illness duration less than two years; 6) hospitalization in the last 6 months; 7) refractory OCD (defined as non response to two SRIs trials, one antidopaminergic augmentation and at least one CBT with ERP trial); 8) patient who did not response to a previous ECT trial; 9) the inability to receive rTMS because of metallic implants, or history of seizures (personal or family history of seizure in first degree relatives); 10) any major medical disease; 11) pregnancy or nursing of an infant; 12) the inability or refusal to provide written informed consent.