demonstrated asymmetric extension. Either one or both anterior ethmoidal arteries were exposed in 65.4% of the cases with supraorbital ethmoidal cells. Since more posterior extension of supraorbital ethmoidal cells is rare, the posterior ethmoidal artery was exposed in only 15 of the cases.Conclusions: The presence of supraorbital ethmoidal cells is not rare and evaluation of their extension is especially important to avoid complications during endoscopic sinus surgery. When the cells extend beyond the ethmoidal arteries, the high ethmoid roof will make these vessels open to laceration during surgical procedure. In order to avoid complications during endoscopic sinus surgery, thorough investigation of paranasal sinus CT scans is crucial.