We describe the results of extensive neurologic evaluation of 290 patients with insulin-dependent diabetes mellitus who came to our institution as potential recipients of a pancreas transplant. Large nerve fibers were evaluated by motor and sensory nerve conduction, small sensory fibers by thermal sensation thresholds, vagal and vasomotor functions by cardiovascular reflexes, and sympathetic sudomotor fibers by silicone imprints and evaporimetry. A scored anamnesis revealed symptoms of neuropathy in 86% of patients; 94% had an abnormal neurologic examination. The most frequently abnormal measurements of motor conduction were the amplitude of the extensor digitorum brevis muscle action potential to peroneal nerve stimulation and the conduction velocity of peroneal and tibial nerves in more than 80% of patients. Sensory nerve action potentials were abnormal in 76% and the distal latency of the sural nerve in 91%. Heart rate variability with deep breathing and during a Valsalva's maneuver was abnormal in 90% and 88%. Sudomotor function was reduced in 59% on the foot. Thermal sensitivity limen was above normal limits in 95% in the foot and 77% in the hand. Composite indexes of the degree of abnormality found for each type of function tested were correlated one with another, but were not predictive of results for any other test. The neuropathy of most patients was symmetric, involving to a similar degree motor, sensory, and autonomic nerves. Thus, diabetic neuropathy is very common and severe among patients who decide to be candidates for pancreas transplantation.