Ultrasonograms of fifteen cases of pathologically proven partial hydatidiform mole at Shimane Medical University Hospital, Japan, occurring from April 1980 to October 1986,were studied. Evaluation was made by a combination of the following sonographic findings : (a) deformity of gestational sac, (b) subchorionic echo-free space, (c) small vesicles in the chorionic tissue, (d) sonographic pattern of the chorionic tissue. Four types were discerned. This study is useful to establish the characteristic sonographic criteria of partial hydatidiform mole.