One hundred and ninety-five operated cases with unilateral maxillary sinus lesions on plain paranasal sinus radiogram at out department from August 1982 through November 1993, were analyzed retrospectively. The following results were obtained. 1) Of 195 cases with unilateral maxillary sinus lesions, inflammation, tumor and cystic disease were 64.6%, 21.0% and 14.4% respectively. 2) The incidence rate of unilateral chronic maxillary sinusitis was 13.5% as compared with bilateral cases. 3) The sex distribution showed 54.9% in male and 45.1% in female, and significant difference among the various diseases. The mucocele was more common in female as 77.8%, while postoperative cheek cyst, maxillary cancer, and inverted papilloma were more common in male as 63.6%, 68.0%, 71.4% respectively. 4) The age distribution was different among some disease. Chronic maxillary sinusitis was most frequent in 2nd to 4th decade as 77.3%, periodontal cyst in 4th to 5th decade as 75.0%, maxillary cancer in over 5th decade as 92.0%, fungal disease and inverted papilloma in over 4th decade as 100%. 5) The most frequently complaining symptom of chronic maxillary sinusitis and inverted papilloma was nasal stuffiness, but epistaxis and facial pain in fungal disease, facial pain and swelling in cystic disease and maxillary cancer. 6) Time lag from onset of clinical symptom to admission was relatively short in unilateral maxillary sinus lesions, especially in fungal disease and maxillary cancer of which less than 1 year of symptom duration was 85.7% and 82.0% respectively. 7) The findings of simple PNS radiogram revealed total hazziness, bony destructive lesions, mucoperiosteal thickening and mucoperiosteal thickening with hazziness as 56.4%, 15.9%, 13.3% and 9.3% respectively. Among the bony destructive lesions, maxillary cancer, postoperative cheek cyst, fungal disease, inverted papilloma and periodontal cyst account for 72.0%, 72.7%, 28.6%, 14.3%, and 25.0% respectively.