Operative exploration of ruptures of the posterior tibial tendon has revealed a relatively constant site of damage just posterior and distal to the medial malleolus. It has been hypothesized that the stress that is applied to the tendon as it passes under the medial malleolus may compromise the vascularity of the tendon in this area, a process that is similar to that described for the supraspinatus tendon. In order to evaluate this possibility, we studied the vascularity of the posterior tibial tendon. We injected twenty-eight cadaveric limbs with an India ink-gelatin mixture and cleared them using a modified Spalteholz technique. The gross external and internal vascularity were drawn, and the specimens were photographed. The vascularity of the tendons was noted to be abundant at the osseous insertion and the musculotendinous function of the tendon. There was a zone of hypovascularity posterior and distal to the medial malleolus in all specimens. The results of this study suggest that relative avascularity and resulting degenerative changes may be predisposing factors in rupture of the posterior tibial tendon, and that they have important implications in terms of the operative management of the rupture.