Circulating endothelial cells (CECs) detach from the intima monolayer after endothelial damages. Their circulating endothelial progenitors (CEPs) represent less than 0.01% of nucleated blood cells. Increased levels of CECs and CEPs have been detected in patients with several types of cancer, suggesting that they could be a useful blood-based marker for detecting a tumor, or for monitoring its clinical course. However, their routine monitoring is time consuming and technically challenging. Here, we present a flow cytometry method for quantifying such cells in a cohort of patients with hemangioblastoma (HB). HB is a rare benign tumor, responsible for 1-2.5% of primary intracranial tumors and up to 10% of spinal cord tumors, and for which no tools are available to predict the onset or recurrence in patients undergoing surgical removal of tumor mass. This method allowed us to accurately quantifying CEC and CEP before and after surgery. CEPs are present at high levels in HB patients than control before intervention, and decrease after tumor removal, suggesting that their percentage could represent a valid tool to monitor the disease onset and recurrence.