Organized hematoma is a benign and non-neoplastic lesion, however, differential diagnosis from neoplastic diseases is always problematic, and patients are often forced to sustain excessive surgical invasion. We retrospectively studied the characteristics of imaging findings of organized hematoma of the maxillary sinus, and estimated the validity and effectiveness of endoscopic sinus surgery for the treatment of this disease. Three patients (2 men and a woman, ranging in age from 50 to 62 years) with organized hematoma of the maxillary sinus who underwent endoscopic sinus surgery were retrospectively analyzed. The diagnosis was provisionally made based on the findings of preoperative computed tomography (CT) and magnetic resonance imaging (MRI), and was confirmed by histopathological examinations of surgical specimens. CT revealed a well-defined expansile mass in the unilateral sinus associated with thinning and expansion of the medial sinus wall in all the cases. On contrast-enhanced images, patchy heterogeneous enhancement was observed. Intermingled low/intermediate/high signal intensity was seen on both T1- and T2-weighted MRI. The lesions were curetted via an endoscopic middle meatal antrostomy with the assistance of a microdebrider. None of the patients received arterial embolization or blood transfusion. Histopathological findings were consistent with those of organized hematoma. Their postoperative courses were uneventful, and all the patients are currently free from disease. We conclude that organized hematoma of the maxillary sinus can be successfully treated by endoscopic sinus surgery under accurate preoperative diagnosis and careful surgical planning.