Auditory brain stem responses were recorded in 20 normoacoustic long-duration Type 1 diabetic patients (duration of diabetes 26 (range 13-46) years, age 44 (25-66) years) with peripheral neuropathy and retinopathy and in 19 sex-matched normoacoustic short-duration Type 1 diabetic patients (duration of diabetes 2 (0-6) years, age 23 (18-50) years) without clinical signs of neuropathy or microangiopathy. Abnormal brain stem auditory evoked responses were demonstrated in 40% of the long-duration and in 5.3% of the short-duration diabetic patients (p less than 0.01). Interpeak latencies Jv-JI and JIII-JI were significantly prolonged in both patient groups compared with the non-diabetic control group (p less than 0.01). Magnetic resonance imaging was performed in 16 of the long-duration patients and in 40 age-matched healthy volunteers on a whole body MR-scanner. Subcortical and/or brain stem lesions with abnormally high signals were seen in 69% of the long-duration Type 1 patients and in 12% of the healthy volunteers (p less than 0.02). Neuropsychological examination including 17 tests for intelligence and cognition were performed in the 20 long-duration Type 1 diabetic patients. The results indicated a performance close to that seen in a control group of healthy age-matched control subjects. Our study demonstrates that a considerable proportion of long-duration Type 1 diabetic patients suffering from retinopathy and peripheral neuropathy additionally have signs but no symptoms of central nervous system affection, diabetic encephalopathy.