In order to compare the adverse effects with the benefits for the characterization of neuropathies after complete sural nerve biopsy, 56 out of 80 patients were examined postoperatively. Preoperatively, sensory deficits were reported by 30 patients (53%), paresthesia and dysesthesia by 18 (32%), and pain by 16 (28%). Twenty-one months after biopsy on the average, persistent loss of sensation was found in 52 patients (93%), persistent paresthesia and dysesthesia in 17 (30%) patients each, and persistent pain in 14 (25%) patients. Pain and paresthesia showed better postoperative improvement than the other sensory symptoms. 15 cases (27%) were diagnosed by histology alone. In 21 cases (37%), nonspecific histological findings contributed valuable diagnostic information. The remaining 20 cases (36%) continued to be unclear despite histology. Demyelinating or mixed-type neuropathies did not yield better results than purely axonal forms. We conclude that sural nerve biopsy is a valuable diagnostic tool, but its side-effects require careful selection of fully informed patients.