We report a rare case of neurofibromatosis type-2 (NF-2) associated with a chest wall schwannoma that was initially suspected of being a breast tumor. The patient was a 28-year-old female who was diagnosed as having NF-2 at 19 years old. At that time, she noticed a mass in the upper lateral region of her left breast but did not have it examined. The mass grew and became painful, and she was therefore referred to our department. Results of the initial examination indicated the possibility of a breast tumor, but a diagnosis of extramammary tumor of the major pectoralis major muscle was made on the basis of the results of ultrasonography and 3-dimensional computed tomography (3D-CT). An endoscope-assisted extirpation of the tumor was performed. Histologically, the tumor was an Antoni type A and B neurilemoma and was diagnosed as a schwannoma.