Objectives: Idiopathic granulomatous mastitis (IGM) is a rare benign disorder of the breast whose aetiology is controversial, and is often misdiagnosed clinically and radiologically as mammary malignancy; as a result, it may be incorrectly treated. Although no standard treatment is available for this chronic disease, surgery with or without corticosteroids has been tried with controversial results. This study discusses the clinical presentation, diagnosis, management, recurrence, and follow-up data of IGM with a review of relevant literature. Methods: From 2009–2012, the Breast Unit at Sultan Qaboos University Hospital, Oman, conducted a clinical study on 20 patients with breast lumps. Their clinical and radiological examinations were indeterminate, and a diagnosis of granulomatous mastitis was established only by histopathology. Results: The majority of the patients were cases of unknown aetiology, who presented with a unilateral breast mass. A few patients had a mass with an abscess, along with axillary lymphadenopathy. A total of 4 patients were suspected of malignancy using radiology. In all patients, sterilised pus was sent for culture and sensitivity. Microscopy showed the characteristic pattern of granulomatous inflammation. All patients were treated with antibiotics for 6 weeks, and the mean follow-up period was 15 months (11–33 months). All patients had complete remission with no further recurrence. Conclusion: This single largest study of cases of IGM in Oman highlights the pitfalls in diagnosing this non-neoplastic disease of unknown aetiology and uncertain pathogenesis. It emphasises IGM's excellent response to antibiotics, which is crucial, as IGM is a disease which is notoriously difficult and controversial to treat.