We studied diabetic central neuropathy(DCN) that is not well-known neurologic disorder. for confirming its existence and then presenting objective diagnostic criteria and methods. Thirtysix diabetics(NIDDM: 30, IDDM: 6), men age 53.1 years, 21 males and 15 females, were com pared with 36 controls, mean age 51.5 years, 18 males and 18 females, electrophysiologically. First, we diagnosed peripheral polyneuropathy(PN) in diabetics by means of Diabetic Neuropathy Staging(DNS) developed at the University of Michigan and classified diabetics into two group; group I indicates diabetics with PN. group II diabetics without PN. Second, we studied central(cortico-cervical and cortico-lumbar) motor conduction time(CMCT) by means of magnetic motor-evoked potential (MEP) and central somatosensory conduction time by means of somatosensory-evoked potentials(SEP) stimulating on median and posterior tibial nerves. There were no significant differences(P>0.05) statistically in cortico-cervical CMCT between diabetics and controls. There were significantly more prolonged(P<0.01) in cortico-lumbar CMCT between diabetics and controls. In median nerve-evoked 3-channel SEP, N13-N20 (cortico-cervical) interpeak latency was significantly more prolonged(P<0.01) in diabetics than controls. In tibial nerve-evoked 2-channel SEP, P38-N22(cortico-lumbar) interpeak latency was significantly more prolonged(P<0.01) in diabetics than controls. In 30 patients(83.3%) of 36 diabetics, the study revealed central conduction delay in view of that above 2 or more abnormalities representing central conduction delay, that is, central neuropathy. In 10 patients(33.3%, M: 7, F:3) of diabetics with central neuropathy(30 patients), even though they had no PN, central conduction delay was revealed. Conclusively, in view of representing central conduction delay in 83.3% of patients, we believer that more active evaluations are needed in diabetics representing nonspecific central neurologic symptoms, for example, psychomotor slowing or cognitive dysfunctions, and MEP and SEP are useful in diagnosing DCN.