AIMS: To determine the causes of ovarian granulomatous inflammation and to discuss the differential diagnoses. METHODS: The pathological features of all ovarian granulomas identified by pathology SNOMED coding in Northern Ireland over a 13 year period were reviewed. Case notes of patients were also reviewed. RESULTS: The most common cause of ovarian granuloma was a foreign body reaction to suture material introduced at a previous operative procedure (15 cases). Other causes were Crohn's disease (four cases), previous diathermy (two cases), tuberculosis (two cases), a necrotising reaction following previous surgery (two cases), endometriosis (one case), and bacterial tubo-ovarian abscess (one case). In five cases, no cause was apparent for the granulomatous inflammation. In these, varying numbers of small, well circumscribed cortical granulomas were present. These cases correspond to so-called "idiopathic" cortical granulomas. CONCLUSION: The study confirms the wide range of conditions which can give rise to ovarian granulomatous inflammation.