Purpose: To report 6 patients with spontaneous orbital hemorrhage in relation to the inferior rectus muscle. Design: Retrospective observational case series. Participants: Six patients with acute onset orbital pain, diplopia, and proptosis referred to the orbital clinic at the Royal Victorian Eye and Ear Hospital, January 1995 through December 2004. Methods: Review of clinical history, imaging studies, and follow-up. Main Outcome Measures: Resolution of proptosis and diplopia and imaging studies of the orbit, including computed tomography (CT),magnetic resonance imaging(MRI), or both. Results: Six patients (4 men, 2 women; mean age, 68 years) were referred with acute onset of unilateral proptosis and diplopi a. None of the patients had a history of bleeding disorder. Visual acuity and intraocular pressure were normal;3 patients showed marked limitation in upgaze on the affected side. Imaging studies of the orbit by CT, MRI, or both showed inferior orbital hemorrhage either within (4 patients) or adjacent to (2 patients) the inferior rectus muscle, possibly within the muscular sheath. Symptoms resolved completely in all but 1 patient, who had persistent diplopia in extreme upgaze. Follow-up CT, MRI, or both showed complete resolution in 3 patients and mild persistent inferior rectus muscle thickening in 2 patients. Conclusions: Acute on set proptosis and diplopia may be secondary to spontaneous orbital hemorrhage within the inferior rectus muscle or its sheath with no other orbital or systemic pathologic features. Symptoms resolved spontaneously over the course of days to weeks, and orbital imaging showed complete resolution o rmild persistent enlargement of the muscle without significant symptoms. Purpose: To report 6 patients with spontaneous orbital hemorrhage in relation to the inferior rectus muscle. Design: Retrospective observational case series. Participants: Six patients with acute onset orbital pain, diplopia, and proptosis referred to the orbital clinic at the Royal Victorian Eye and Ear Hospital, January 1995 through December 2004. Methods: Review of clinical history, imaging studies, and follow-up. Main Outcome Measures: Resolution of proptosis and diplopia and imaging studies of the orbit, including computed tomography (CT), magnetic resonance imaging None of the patients had a history of bleeding disorder. Visual acuity and (MRI), or both. Results: Six patients (4 men, 2 women; mean age, 68 years) were referred with acute onset of unilateral proptosis and diplopi a. 3 patients showed marked limitation in upgaze on the affected side. Imaging studies of the orbit by CT, MRI, or both showed inferior orbital hemorrhage either within (4 pa Tumors) or adjacent to (2 patients) the inferior rectus muscle, possibly within the muscular sheath. possibly Symptoms resolved in all but 1 patient, who had persistent diplopia in extreme upgaze. Follow-up CT, MRI, or both showed complete resolution in 3 patients and mild persistent inferior rectus muscle thickening in 2 patients. Conclusions: Acute on set proptosis and diplopia may be secondary to spontaneous orbital hemorrhage within the inferior rectus muscle or its sheath with no other orbital or systemic pathologic features. Symptoms resolved spontaneously over the course of days to weeks, and orbital imaging showed complete resolution o rmild persistent enlargement of the muscle without significant symptoms.