Of 4,546 patients examined, 73 had mucosal cysts in one or both maxillary sinuses. Distribution between sinuses was approximately equal. Most cysts appeared to arise from the floor of the sinus. Almost half of those with cysts reported an allergy of some type. No significant relationship to other medical problems was found. About one half of the patients had identifiable periodontal disease, and a trend toward larger cysts with increasingly severe periodontal disease was noted. Thirty-four patients were re-examined after 2 to 38 months, and 21 still had cysts unchanged in size. A trend toward higher occurrence of cysts during certain times of the year was also noted.