We examined uptake of 2-[(18)F]-fluoro-2-deoxy-D-glucose (FDG) using positron emission tomography (PET) into the bilateral shoulder muscles of four patients before and after unilateral rotator cuff repair. The relative ratio of the subtracted standardized uptake value on the supraspinatus with a torn supraspinatus tendon to that of the subscapularis on the ipsilateral side was significantly lower than that on the normal side (0.69 +/- 0.05 versus 1.06 +/- 0.36). The relative ratio of the infraspinatus on the rupture side was also significantly lower than that on the normal side (0.91 +/- 0.09 versus 1.41 +/- 0.35). However, by 6 months postoperative, the reduced glucose metabolism in these muscles had recovered to the same levels as those on the normal side. As indicated by FDG PET, muscle metabolism in rotator cuff tears was reduced, subsequently recovering to the level of the normal side after operative repair.