We evaluated 37 patients with surgically treated Achilles tendon disorders, comparing findings of preoperative ultrasonography with findings at surgery, to investigate the reliability of ultrasonography in diagnosing partial ruptures of the Achilles tendon. Discontinuity of tendon fibers, focal sonolucencies, and localized tendon swelling were positive findings suggestive of partial ruptures. We found the use of ultrasonography to be safe and reliable, with a sensitivity of 0.94, a specificity of 1.00, and an overall accuracy of 0.95.