The authors reviewed the electroencephalographic findings relevant to a casuistry of 136 cerebral tumours in paediatric age and correlated them with the anatomic site of the neoplasias, as checked on the operating table, and with clinical symptomatology. The casuistry, as concerns the site of the tumours, consists of 32 cases with a hemispheric localisation, 35 localized on the median line (suprasellar tumours, tumours of the 3rd ventricle, tumours of the basal nuclei and tumours of the pineal region) and 68 cases of tumours of the cerebellar fossa. E.E.G. proved normal in 9.3% of the patients with a hemispheric tumour, 17.1% of those with median tumours and in 23.1% of the tumours of the cerebellar fossa. 12.5% of the cases with a hemispheric tumour showed a general widespread alteration of the electroencephalogram, which was also traceable in 20% of the deep seated tumours and 13% of the subtentorial tumours. A focal E.E.G. finding with polymorphic delta waves was detected in 62.5% of the tumours with a hemispheric localisation, as compared to 14.2% of the deep seated and 28% of the subtentorial ones. Finally, in the three groups, intermittent slow waves were detected respectively in 46.8%, 51.4% and 72.4% of the cases. Related with clinical conditions, in the presence of endocranial hypertension, a clear prevalence of general widespread alteration and of intermittent activities were detected. The authors discuss the diagnostic value of each E.E.G. finding in cerebral tumours with particular attention to localizing value of focal polymorphic delta waves and to the meaning of intermittent slow waves which, in paediatric age, show a clear prevalence in the posterior cerebral areas.