A 34-year-old man with neurofibromatosis type 1 (von Recklinghausen's disease) was examined by 201TlCl and 99mTc-tetrofosmin scintigraphies. Hypervascularity was observed in the largest tumor of the right thigh. The tumor was also depicted on both scintigrams. Tumorectomy was performed and the pathologic examination revealed it to be a neurofibroma measuring 10 x 7 x 4 cm in size. These findings suggested that 201TlCl and 99mTc-tetrofosmin scintigraphies generally were unable to distinguish malignant from benign neurofibromas with certainty.