A consecutive series of 90 patients undergoing endoscopic intranasal ethmoidectomy was reviewed. There were 26 complications (29%) in 19 patients in this group. Eight complications (8%) including CSF leak, temporary blindness, and hemorrhage were considered major with the latter occurring most commonly. Synechiae were the most commonly occurring minor complications. Endoscopic nasal sinus surgery performed by inexperienced operators carries with it the same risks and complications as traditional intranasal sinus surgery. Any surgeon who does not routinely perform traditional intranasal ethmoidectomy should accrue endoscopic experience through appropriate didactic training and multiple cadaver dissections (akin to otologic training).