Forty-two evaluable pediatric patients with a variety of recurrent primary brain tumors participated in a phase II ifosfamide trial. Their mean age was 10 years. All patients were treated with ifosfamide, 3 g/m2/day for 2 days every 2 weeks. Response was assessed on clinical and radiological criteria after at least 2 courses of therapy. The overall response rate was 12% (5/42). One complete and 2 partial responses were documented in 21 patients with medulloblastoma. A partial response was demonstrated in 1 patient with primitive neurectodermal tumor (PNET) and in 1 patient with ependymoma. No activity was observed in astrocytic tumors. Toxicity was primarily neurologic (16 out of 54 patients, 30%). Hematological toxicity, without severe morbidity, was encountered in 9% of courses (16/179). Ifosfamide, administered at this dose regimen has modest efficacy in the treatment of recurrent childhood medulloblastoma and ependymoma and appears inactive for gliomas. Further trials with other dose schedules are necessary to assess the activity of this drug. However, according to the neurotoxicity observed in our trial, we would not recommend building a protocol using ifosfamide for highly progressive brain tumors.