A laboratory study was performed to evaluate the histopathological features of the macroscopically intact portion of the Achilles tendon in patients undergoing surgery for an acute rupture of the Achilles tendon. Tendon samples were harvested from 29 individuals (21 men, 8 women; mean age: 46 ± 12) who underwent repair of an Achilles tendon tear tear, and from 11 male patients who died of cardiovascular events (mean age: 61). Three pieces of tendon were harvested: at the rupture site, 4 cm proximal to the site of rupture, 1 cm proximal to the insertion of the Achilles tendon on the calcaneum. Slides were assessed using a semiquantitative grading scale assessing fiber structure and arrangement, rounding of the nuclei, regional variations in cellularity, increased vascularity, decreased collagen stainability, and hyalinization. Intra-observer reliability of the subscore readings was calculated. The pathological features were significantly more pronounced in the samples taken from the site of rupture than in the samples taken proximally and distal to it (0.008 < P < 0.01). There were no significant differences in the mean pathologic sum-scores in the samples taken proximally and distal to the site of rupture. Unruptured Achilles tendons, even at an advanced age, and ruptured Achilles tendons are clearly part of two distinct populations, with the latter demonstrating histopathological evidence of failed healing response even in areas macroscopically normal.