A 56-year-old Japanese woman was treated surgically for orbital paraganglioma. She had had proptosis of the left eye and lowered visual acuity. Papilledema and many retinochoroidal folds were seen. CT-scan demonstrated a tumor shadow on the optic nerve in the muscle cone. Tumor extirpation by Kronlein-Berke's procedure resulted in complete loss of vision due to surgical damage to the optic nerve. The previously reported 24 cases of orbital paraganglioma are reviewed. According to these clinical descriptions, orbital paragangliomas occur unilaterally in males and females, at any age, especially over 50 years. Objective signs are unilateral proptosis, lowered visual acuity and occasionally papilledema, but these are not specific for orbital paraganglioma. Orbital paraganglioma is apt to recur. Clusters of tumor cells were arranged like islands or nests in the connective tissues. The ultrastructure of the tumor cells closely resembled that of paragangliomas of the carotid body and glomus jugulare. In the present case the chief cells contained chromaffin granules, but only a very few. In addition to the ultrastructural resemblance of the tumor presented here to carotid body and glomus jugulare paragangliomas, the presence of chromaffin granules, even though scarce, confirmed that the present tumor is a paraganglioma and strongly suggests that the human orbit contains paraganglionic tissue.