Rupture of the medial head of the gastrocnemius muscle, or tennis leg, is a common lesion affecting middle-aged persons. An imaging examination may be needed to rule out other diseases and assess the severity of the tear. We reviewed the sonographic images of 65 patients with clinically suspected tennis leg. Fifty-one partial and 14 complete tears were diagnosed. Twenty-five patients had follow-up examinations (15 days to 24 months; mean, 45 days). The torn muscle fibers, hematoma, and the reparative process were appreciated by ultrasonography. Ultrasonography may be a useful noninvasive, low-cost modality for diagnosis and follow-up of tennis leg.