During the period 1978-1981, among 1280 (0-12 months old) infants suffering from consequences of various pre- and perinatal cerebral lesions, positive neuroradiological changes were found in 148 cases. Of these, 56 proved to be real subdural effusions with elevated ICP and increased protein content. Periodical transfontanellar taps and drainage were effective in 49 cases. A neurosurgical operation was performed in 7 infants because of the poor effect of the above treatment. In these 7 infants the encapsulation process was nearly complete. Early chronic subdural effusion exerts a devastating influence on the maturing brain partly by the high ICP. Early treatment often cures the process and major surgery is not needed. Early neurorehabilitation and habilitation coordinated with elimination of the effusion is the method of choice. Prudence is recommended in selecting the appropriate cases for instrumental therapy because some small effusions and fluid accumulations may disappear by the end of the first year.