A follow-up study was carried out of the clinical symptoms and the radiological and histological alterations in five cases of neurofibromatosis (Recklinghausen's disease) with onset during early childhood. The clinical manifestation of the disease was predominantly restricted to the face. In the histological ultrastructural investigation different types of neurofibroma were detected (plexiform neurofibroma, argyrophilic neurofibroma and diffuse neurofibrma). Preliminary results are presented on the basis of a correlation between the clinical findings and the histological types of neurofibroma with special reference to the demarcation of the tumours, recurrence following surgical removal and the prognosis as to the clinical course of the disease. Nevertheless, definite conclusions will be possible only by continuous observation of a larger number of patients by means of standardized clinical, radiological and histological methods of investigation.