To investigate the relationship between the shoulder gradient and acromiohumeral interval of both shoulders in patients with unilateral shoulder impingement syndrome.Using the angulometer, we measured the shoulder gradient in patients with unilateral shoulder impingement syndrome in a standing position. Using the radiography, we measured the acromiohumeral interval and the angle between a vertical line and a line connecting a superior angle with an inferior angle of the scapula.In patients with unilateral shoulder impingement syndrome, the frequency of shoulder impingement syndrome was 76.2% (16 of 21) on the side of the relatively lower shoulder. The mean acromiohumeral interval on the side of the lower shoulder was 10.03±1.28 mm, compared with 10.46±1.50 mm for the higher shoulder. The angle between a vertical line and a line connecting a superior angle with an inferior angle of the scapular of the side of the lower shoulder was -0.31±3.73 degrees, compared with 3.85±4.42 degrees for the higher shoulder.The frequency of shoulder impingement syndrome was significantly higher on the side of the relatively lower shoulder, and there is no significant difference in the acromiohumeral interval between the side of the lower shoulder and that of the higher shoulder. In patients with unilateral shoulder impingement syndrome, the scapular on the side of lower shoulder was more rotated downward than on the side of the higher shoulder.