The Purpose of this study is to detect morphological changes of the maxilla following the operation of paranasal sinuses in the orthopantomogram. 1) The measurement of the angle set up by two reference lines which represent posterior aspect of the maxilla and skull base was made. 2) The mean angle in the post-operative patients showed significantly smaller than that in the normal subjects. 3) The forms of posterior aspect of maxilla were classified into 5 types. (flat, convex, concave, uneven and obliterated.) 4) In contrast with the convex type in the majority of normal subjects, approximately half of the post-operative patients showed the concave type. 5) These results may suggest that the superior part of the posterior aspect of the maxilla tend to depress following the operation of these paranasal sinuses.