Introduction:Tendons may rarely be ossified. The calcaneal tendon (CT) is the largest in the body. The incidence and mechanism of ossification of CT is not known.Material and Methods:We carried out a morphological, radiological, histological, and immunohistochemical study on the CT of 50 (30 – male and 20 – female) human cadavers.Results:The mean length (cm) of the CT was 27.60 ± 2.30 (right) and 27.51 ± 2.60 (left) in males and 25.43 ± 0.77 on both sides in females. The contribution to the formation of the CT from the two heads of gastrocnemius muscle was greater from medial head in 84%, lateral head in 12%, and equal in 4%. On screening the CT by C-arm radiography, slight opacification at the site of insertion of CT (bilaterally) was noted in an elderly male. Large, bilateral opacification was seen in another elderly male cadaver. Well-defined lamellar bone with osteocytes lying in lacunae and bone marrow amid the tendon collagenous tissue was noted in hematoxylin- and eosin-stained sections. The osteocytes expressed hypoxia-induced factor 1 alpha.Discussion and Conclusion:In this study, we confirmed that the radiological opacification in the CT was ossification that may have been triggered by hypoxia.