Dysthyroid orbitopathy occurs in thyroid diseases, such as Graves’ disease, and causes proptosis, eyelid swelling, diplopia, and visual loss. Treatment with both corticosteroids and orbital irradiation is usually recommended in the active inflammatory phases, but some patients show a poor response. Either orbital decompression surgery or eyelid surgery is the preferred treatment in the non-responsive cases or in the patients in the inactive phase who want either cosmetic or rehabilitative surgery. We report on three patients with dysthyroid orbitopathy who underwent endoscopic transnasal orbital decompression. The lamina papyracea of the ethmoid bone and the medial portion of the orbital floor were drilled out and removed. Two horizontal incisions were made in the periorbital periosteum along the superior and inferior margins of the medial rectus muscle. The orbital contents were manually prolapsed into the space in the ethmoid and maxillary sinuses. The first patient suffered visual loss due to compressive optic neuropathy. After systemic steroid treatment, recovery of the eyesight was restored. Visual acuity remarkably improved after orbital decompression. The two other patients suffered proptosis, diplopia, and dry eye. Systemic steroid treatment and orbital irradiation therapy prior to surgery did not improve these symptoms. After orbital decompression, the patients also showed improvement in proptosis and in subjective symptoms.Although endoscopic transnasal orbital decompression has become more widely used in western countries since it was first introduced in 1990, few cases have been reported in Japan. We suggest that the procedure can be performed safely without external incision and that it provides otolaryngologists with an additional effective treatment option.