BACKGROUND AND IMPORTANCE: Pial arteriovenous fistulas (AVFs) of the brain are treacherous lesions that can be challenging to treat because of high risk of hemorrhage. We report on a rare case of a pial AVF with a giant venous varix as a draining vein treated successfully with flow-directed balloon-assisted Onyx embolization. CLINICAL PRESENTATION: A 56-year-old female with headaches underwent brain magnetic resonance imaging, which demonstrated a 4 cm aneurysmal malformation in the right temporal lobe. A diagnostic cerebral angiogram demonstrated a right temporal pial AVF fed by an enlarged right posterior cerebral artery with drainage into a giant venous varix. Onyx embolization was curative using a flow-directed Scepter balloon catheter. CONCLUSION: Flow-directed balloon-assisted Onyx embolization can be highly successful for the curative embolization of pial AVFs. Balloon application changes the nature of the lesion from high-flow-high risk to no-flow-low-risk. Using a flow-directed technique with balloon microcatheters may help minimize the risk of intracranial vascular injury.