In a strictly selected material of 80 patients, who were all outpatients of a special nephrological clinic, with chronic renal insufficiency with retention values of 1.4-14.5 mg% serum creatinine, an EEG was done besides thorough neurological and internal examinations. In 21 cases (26.2%) a pathological EEG in the form of background slowing and general dysrhythmia. There was a tendency to increase in pathological EEG findings in correlation with increase of the retention values. The patients with pathological EEG had on the average a creatinine value of 5.89 mg%, those without EEG findings had an average creatinine value of 3.98 mg%. The difference is statistically significant (alpha less than or equal to 0.015). It is notable that there is a statistical correlation (alpha less than or equal to 0.005) between the presence of pathological EEG and the motor conduction velocity of the peroneal nerve: only 12% of the patients with a conduction velocity of less than 43 m/sec had a pathological EEG while 60% of the patients with a conduction velocity of more than 43 m/sec had EEG findings. No statistical correlation were found between the EEG changes and other neurological and internal signs and symptoms, including cardiovascular findings like the blood pressure.