We report a patient with a dissecting aortic aneurysm associated with polymyalgia rheumatica (PMR). The patient is a 55-year-old Japanese man without a history of hypertension, diabetes mellitus and syphilis. He was admitted to an emergency hospital because of severe back pain, and was diagnosed as having a dissecting aneurysm of the descending aorta. After the admission, he began to notice severe muscle pain in his bilateral shoulder. Although his back pain gradually improved, his muscle pain progressively worsened, and his lower extremities were also involved. Then, he was introduced to our hospital. On neurological examination, he was alert and oriented. His cranial nerves were all intact. There was no muscle weakness nor sensory disturbance. Laboratory studies revealed that his erhythrocyte sedimentation rate was extremely high without elevation of the serum level of creatine phoshpokinase, rheumatoid factors and c-reactive protein. He was diagnosed as having PMR, and oral administration of prednisolone++ was started. Within several days, his muscle pain dramatically disappeared. As is known, there is a close relationship between PMR and temporal arteritis of giant cell arteritis. In general, PMR is a benign disease and responds well to steroid therapy, and prevalence of the giant cell arteritis is low in Japanese people. However, it should be kept in mind that the dissecting aneurysm is a relevant, severe complication of PMR because arteritis can be latently present in PMR.