During intra-arterial (IA) chemotherapy of brain tumors, the initial vessels chosen for infusion are based on the vascular distribution of the tumor as revealed by CT or MR imaging. However, angiography may reveal details of vascular anatomy that require an alteration of the vessel infusion plan. The incidence of infusional alterations and the underlying vascular anatomy involved remains unknown in patients with brain tumors undergoing IA chemotherapy. To evaluate this question, we performed a chart, CT/MRI, and angiography review of brain tumor patients receiving IA chemotherapy. Seventy-eight patients were identified with primary (39) and metastatic (39) brain tumors. The cohort consisted of 40 males and 38 females, with a mean age of 47.8 years. During the course of IA treatment, angiographic review identified 5 patients (6.4%) that required an alteration of the vessel infusion plan. In three cases, angiography demonstrated more substantial perfusion of the tumor from a different arterial supply. In two cases, angiography revealed variations in normal anatomy associated with unexpected tumor perfusion. Careful interpretation of angiography at the initiation of each cycle of IA chemotherapy is very important to verify that the appropriate vessels have been chosen for drug infusion, in order to maximize regional dose intensity. In our series, the angiography results necessitated an alteration of the infusion plan in 6.4% of the patient cohort.