Some patients with chronic sinusitis do not respond to conservative therapy or radical surgery because of interfering factors. Others occasionally develop postoperative maxillary cysts as a later complication. Various methods of solving these problems have been reported.We treated 24 lesions in 22 patients with chronic sinusitis by cryosurgery from April, 1975, to September, 1985, at the Cryosurgical Clinic of Kobe University Hospital. These patients had not been improved by two months or more conservative therapy. Some of them had had endonasal surgery (polypectomy, partial ethmoidectomy, etc.) prior to conservative therapy.The cryosurgical unit was modified so as to be suitable for maxillary sinus lesions. First a small hole was drilled through the lateral wall of the meatus nasi inferior or the fossa canina, and a special probe was inserted through this hole to freeze the inflamed mucous membrane of the maxillary sinus by liquid nitrogen spray.The results were evaluated by morphological and functional examinations. Of the 24 lesions 15 (62.5%) were improved. It is concluded that cryosurgery is a valuable therapy for chronic sinusitis (mainly of the maxillary sinus).