The risk to developing a neoplasm is increased when associated to a patient phakomatosis (Recklinghausen neurofibromatosis, Bourneville's tuberous sclerosis). We analysed 6 cases with phakomatosis and tumours, admitted in the Department of Oncopediatry, between 1993-1998; five of these children had neurofibromatosis and one Bourneville's disease. The associated tumours were hematologic malignancies (juvenile myeloid chronic leukemia) and solid tumors (rhabdomyosarcoma, hepatic carcinoma, CNS tumour, NHL optic glioma). The diagnosis was confirmed by microscopic examination of the bioptic material in all cases. Tumoral staging was performed by clinics, biology and imagistic investigations. All cases had extensive and aggressive tumours at the moment of diagnosis, We noticed a poor response and an early relapse after chemotherapy. A special follow-up and a different management has to be established for the patients with phakomatosis, in order to have a good oncological prophylaxis.