In order to evaluate central nervous system disorders in myotonic dystrophy (MyD), neuron-specific enolase (NSE), S-100b protein and creatine kinase BB (CK-BB) isoenzyme were measured using enzyme immunoassay in MyD. Intelligence quotient (IQ) test (WAIS, 17 cases), electro-encephalography (17 cases) and brain computed tomography (18 cases) were examined. In patients with MyD, NSE level was significantly elevated in comparison with 25 age-sex matched control subjects. In some cases of MyD levels of S-100b protein and CK-BB in CSF were elevated. IQ test disclosed intellectual impairment in 70.6% of the patients examined and EEG study demonstrated slowing of basic rhythm in the majority of the cases. On brain CT both enlarged ventricles and dilated sulci were commonly found. The results of the present study suggest that in MyD the CNS is involved not only functionally but structurally as well. Since NSE, S-100b and CK-BB are localized in neuronal and glia cells, their elevated levels in CSF indicate existence of organic lesions in the central nervous tissue in patients with MyD.