Diademodon and Cynognathus were contemporary cynodonts that lived during the Early to Middle Triassic. Their fossilized remains are found in the same deposits and, in the absence of diagnostic cranial material, the postcranial skeletons of these animals are considered indistinguishable from one another. In this study the bone histology of Diademodon and Cynognathus was examined, using thin sections of several long bone elements. Distinctive histological patterns were recognized for each genus: the cortex of Diademodon is zonal, consisting of alternating bands of fibro-lamellar and lamellar bone tissue, whereas that of Cynognathus consists of uninterrupted fibro-lamellar bone tissue. The bone histology indicates that Diademodon had a cyclical growth strategy whereas Cynognathus grew continually, at a constant, rapid rate throughout the year. Quantification of the vascularization of the compacta using image analysis, has shown that the bone tissue of Cynognathus is significantly more vascularized than that of Diademodon. The marked differences in their bone histology and vascularization, have permitted the generic identification and distinction of postcranial material (limb bones) previously categorized as either Cynognathus or Diademodon. This study of Diademodon and Cynognathus is the first detailed examination of the bone histology of representatives of the Triassic Cynodontia. The characteristic patterns of bone histology in Diademodon and Cynognathus have directly revealed information about their growth strategies and has demonstrated the use of bone histology to distinguish between the genera when associated cranial material is absent.