We investigated the frequency of subclinical trigeminal and facial nerve involvement in 40 patients with diabetes mellitus and without clinical signs of cranial nerve lesions. 60% of the patients had distal symmetric sensory polyneuropathy which was confirmed by nerve conduction studies. Trigeminal and facial nerve functions were evaluated electrophysiologically using the blink-reflex R1 component (BlinkR-R1), masseter reflex (MassR), the first exteroceptive suppression of the masseter muscle (Mass-ES1), and distal motor latency of the facial nerve (DML VII). Latencies were significantly prolonged for the BlinkR-R1 (p < 0.0001), the Mass-ES1 (p < 0.05), and DML VII (p < 0.005) in diabetics compared with controls. No significant difference was found for the MassR. Prolonged latencies (> mean + 2.5 SD of age-matched controls) were demonstrated for the Mass-ES1 in 12.5%, BlinkR-R1 in 10%, DML VII in 6.2%, and MassR in 5% in individual of patients. Our findings indicate that trigeminal and facial nerve involvement is not infrequent in diabetics, although it is significantly less frequent than limb nerve involvement.