The purpose of this study was to clarify the stress distribution in the rotator cuff tendon with 3 types of partial-thickness tears by use of 2-dimensional finite element analysis. In the finite element model of the normal human shoulder, a tendon defect was created on the articular surface, on the bursal surface, or in the midsubstance close to the insertion. A tensile force was applied to the proximal end of the tendon, and the stress distribution was calculated. In all 3 types of tears, a high stress concentration appeared around the articular surface at the insertion and at the site of the tear, which extended proximally. The maximum value of the von Mises stress increased with the presence of a partial-thickness tear. With the arm in abduction, a high stress concentration was also observed around the site of the tear. These biomechanical conditions of the supraspinatus tendon may eventually lead to a full-thickness tear at the critical zone.