Spinal somatosensory evoked potentials to stimulation of the peroneal nerves in the popliteal fossa were recorded from 46 insulin-dependent neurologically normal patients with juvenile diabetes. Conduction velocities of these potentials were determined over proximal peroneal nerve, cauda equina, and spinal cord and were compared with those obtained from 46 age-matched control subjects. Mean values for overall spinal conduction velocity (L3-C7 spines) and conduction velocity over rostral spinal cord (T6-C7 spines) and peroneal nerve-cauda equina (stimulus to L3 spine) were lower in the diabetic group (p less than 0.001). Peripheral nerve conduction velocity alone was slow in 5 patients, and spinal conduction velocity was slow in 8; in 2 patients both peripheral and spinal velocities were slow. This study suggests that in addition to impairment of peripheral nerve function, patients with juvenile diabetes without clinical evidence of neurological involvement can have a defect in spinal afferent transmission.