The purpose of this study was to determine the safety of tinzaparin for deep vein thrombosis prophylaxis in newly diagnosed grade III-IV malignant glioma patients. Patients were initiated on daily tinzaparin at a fixed dose of 4,500 IU subcutaneously between 48 h and 4 weeks post-operative for planned duration of 12 months. During chemotherapy cycles, blood counts were monitored weekly and tinzaparin was held if the platelet count decreased to <50,000 and was re-initiated at a platelet count >100,000. Forty patients were enrolled into the study, 35 with glioblastoma multiforme and 5 with anaplastic astrocytoma. Possible attributable toxicity was limited to two patients who developed CNS hemorrhages (one grade 1 and one grade 2) and one patient with an increase in liver enzymes (grade 3). There were no patients with a grade 4 or 5 CNS hemorrhages or systemic hemorrhages >or=grade 2. The median time on prophylactic tinzaparin was 161 days (range of 5 to 601 days). One patient developed a deep venous thrombosis while taking tinzaparin, and three patients developed thromboembolic complications while off tinzaparin. Tinzaparin at a fixed prophylactic dose is safe and may decrease the incidence of thromboembolic complications in brain tumor patients.