A review of 63 magnetic resonance images of 86 ankles was performed. (There were 23 bilateral studies.) A contiguous fascial band from the deep posterior compartment to the Achilles tendon watershed region was noted in 83 ankles. This fascial band enveloped the watershed region, coursing from the flexor (lacinate) ligament medially, to the peroneal retinaculum laterally. This band was absent in three patients who were scanned, two of whom sustained a complete Achilles tendon rupture, while the third had previously undergone peritenolysis. Forty cadaveric specimens with no known Achilles tendon pathology were evaluated for presence of this structure. An organized fascial band existed in all of these specimens. This previously undescribed structure is termed the "watershed band" and may have surgical significance.