Transnasal ethmoidectomy is a current treatment in selected cases of nasal polyposis, and with its complicated anatomy offers a proper opportunity for microsurgery. Ten years' experience of microsurgical ethmoidectomy in 155 patients with nasal polyposis is reported. The surgical anatomy of the ethmoid sinus is reviewed with attention to the requirements of the microsurgical approach, and the operative procedure is described. The microsurgical approach is discussed both as a part of the treatment of nasal polyposis and as a new development in rhinologic surgery. Advantages of the technique are the objective safety against risks of the ethmoid area and enhanced sense of security for the surgeon.