Four children, who were treated for supratentorial primitive neuro-ectodermal tumours between 1986 and 1995 at Kyushu University Hospital, are here presented. The initial characteristic symptoms and signs of these patients included vomiting and headache, followed by motor weakness. All patients underwent direct surgery for their tumours while 2 also received a course of postoperative radio-therapy. After these treatments, 3 died within 4 months after diagnosis, whereas one infant, who underwent a total removal of the tumour but had no adjuvant therapy, is still alive after a follow-up period of 4 years. Most of the tumour cells of these 4 cases were poorly differentiated neuro-ectodermal cells, but some also showed variable differentiation along the glial and/or neuronal lines. While such differentiation had no impact on the clinical course of the patients, the malignant potential as assessed by the percentage of MIB1-positive cells showed a good correlation with the clinical features; the 3 cases with a rapid clinical course had MIB1 staining indices of more than 2%, and one case, who survived more than 4 years, had the same indices of 0.2% as found in benign tumours. Although "PNETs" of Hart and Earl share certain clinical features, they may be a group of tumours heterogeneous in their origins, histogenesis, and biological behaviours.