Meningiomas represent 18-20% of all intracranial tumors and have a 10-year recurrence rate of 20-50%, despite aggressive surgery and irradiation. In addition, many tumors are not amenable to surgery due to their deep location or proximity to delicate structures. Chemotherapy is being explored as another potential treatment option for unresectable or refractory meningiomas. Hydroxyurea is an agent that inhibits ribonucleotide reductase and can induce apoptosis in meningioma cell cultures and animal models. We have placed 17 patients with unresectable or residual meningioma on hydroxyurea chemotherapy (20 mg/kg/d orally). The mean age of our cohort was 57.2 years; 13 patients were female. Eleven patients had actively growing tumors or neurological progression at the onset of chemotherapy. Sixteen patients were evaluable for response. Fourteen of the 16 patients (88%) responded with stable disease ranging from 20 to 144+ weeks (median 80 weeks; 10 patients still accruing time). Three of the responders progressed after 20, 36, and 56 weeks, respectively. Two patients had progressive disease after 10 weeks. Toxicity was hematologic in most patients; leukopenia was most common. Nine patients (53%) required dosage reductions (250-500 mg/d) secondary to hematologic toxicity. Hydroxyurea appears to have modest activity against meningiomas and should be considered in patients with unresectable tumors or large residual tumors following surgical resection.