The primary aim of this study is to report the long-term outcome of pineal and suprasellar germinoma after stereotactic biopsy and whole brain radiotherapy. The second purpose is to report an investigation of the biological features and cell kinetics of this peculiar and enigmatic brain tumour. Of 34 supratentorial germ cell tumours diagnosed and treated between 1980 and 1993, 20 patients were found to be affected by true germinoma localized in the pineal and/or suprasellar regions. The diagnosis was achieved by stereotactic biopsy in all cases. In 14 patients, the potential proliferative activity of the tumour was investigated by (3H)thymidine in vitro binding and labelling index determination. Chorionic gonadotropin, alpha-fetoprotein and embryonal carcinoma antigen were negative in the cerebrospinal fluid of these patients. All but 1 patient underwent whole brain radiotherapy. Clinical and neuroradiological follow-up ranged between 3 and 13 years (mean 8). Complete clinical and neuroradiological recovery was achieved in all patients after treatment. Fatal recurrences owing to neuraxis dissemination occurred in three cases. The labelling index in the whole series ranged between 0.1 and 5% (median 2.5). Only syncytiotrophoblastic cells had proliferative activity, while none of the lymphoid-like cells showed thymidine labelling.