The purpose of the present study was to assess the validity of the Thompson sign and determine whether the deep flexors of the foot can produce a falsely intact Achilles tendon.Ten unmatched above-the-knee lower extremity cadaveric specimens were studied. In group 1, the Achilles tendon was sectioned into 25% increments. The Thompson maneuver was performed after each sequential sectioning of the Achilles tendon, including after it had been completely sectioned. If the Thompson sign was still intact after complete release of the Achilles tendon, we proceeded to release the tendon, and tendon flexor hallucis longus, flexor digitorum longus, and posterior tibial tendons. The Thompson test was performed after the release of each tendon. In group 2, the tendon releases were performed in a reverse order to that of group 1, with the Thompson test performed after each release. In group 1, the Thompson sign remained intact in all specimens after sectioning of 25%, 50%, and 75% of the tendon. After complete (100%) release of the tendon, the Thompson sign was absent in all specimens. In group 2, the Thompson sign remained intact after sectioning of the posterior tibial, flexor digitorum longus, and flexor hallucis longus tendons in all specimens. The Thompson sign remained intact in all specimens after sectioning of 25%, 50%, and 75% of the Achilles tendon. After complete release of the tendon, the Thompson sign was absent in all specimens.The Thompson test is an accurate clinical test for diagnosing complete Achilles tendon ruptures. However, it might not be a useful test for diagnosing partial Achilles tendon ruptures. Our findings also call into question the usefulness of the Thompson test in the intraoperative setting.