Over a 17-year period, 56 patients with 57 tumors involving the brachial plexus were operated upon. The 40 neural sheath tumors included 26 neurofibromas, 8 schwannomas, 4 malignant neural sheath tumors, 1 fibrosarcoma, and 1 meningioma. Nine of the neurofibromas were associated with von Recklinghausen's disease (VRD), and 2 others were what was termed regionalized neurofibromatosis characterized by involvement of one limb with extension along the course of one or more plexus elements. Seventeen tumors were not of neural sheath origin; 7 were benign and 10 were metastatic malignant tumors compressing or invading the plexus. Benign neurofibromas and malignant sheath tumors almost always presented with pain or functional neural deficit, whereas schwannomas often presented with a palpable mass as their only initial symptom. Patients with solitary neurofibromas were significantly older, often female, and more likely to have tumor on the right side than patients with schwannomas, malignant neural sheath tumors, or neurofibromas associated with VRD. Solitary neurofibromas could often be totally resected without added deficit by sacrificing fascicles entering and leaving tumor that were determined to be "nonfunctional" by intraoperative nerve action potential recordings. Resection of neurofibromas associated with VRD sometimes but not always resulted in significant loss. Operation is nonetheless recommended, especially when malignancy is suspected because of rapidly increasing size, when severe pain or neural deficit is present, or when compression of adjacent plexus elements is a concern. Schwannomas and benign non-neural sheath tumors can usually be extirpated without damage to plexus elements. Forequarter amputation is advised for malignant intrinsic tumors involving distal plexus elements even though gross total resection seems feasible.