Neurofibromatosis type 1 (NF-1) is an autosomal dominant disorder that has three major features: multiple neural tumors, Gafe-au-lait spots, and pigmented iris hamartomas (Lisch nodules). The purpose of this case report is to advise physicians of the danger associated with the progression of fast-onset massive hemorrhage to hemodynamic instability, which mandates rapid treatment to prevent the development of a life-threatening condition. A 64-yr-old woman with NF-1 was admitted to the Emergency Department (ED) because of a rapidly growing, 10 x 5 x 3 cm-sized mass on the left back area. She had previously undergone surgery for a large subcutaneous hematoma, which had developed on her right back area 30 yr before. She became hemodynamically unstable with hypotension during the next 3 hr after admission to ED. Resuscitation and blood transfusion were done, and the hematoma was surgically removed. The mass presented as a subcutaneous, massive hematoma with pathologic findings of neurofibroma. We report a case of NF-1 that presented as recurrent, massive, subcutaneous hemorrhage on the back region combined with hypovolemic shock.