Analysis of a case of presumed hematogenous septic arthritis and osteomyelitis involving the elbow, distal humerus, and proximal radius and ulna in a leatherback turtle (Dermochelys coriacea) showed the chondro-osseous response to be similar to the diseases in skeletally immature humans and terrestrial mammals (both spontaneous and experimental). This particular reptile has bone that is similar to mammalian bone. The infection had partially destroyed the distal humeral, proximal ulnar and proximal radial joint surfaces and epiphyseal cartilages. The elbow was filled with a fibrovascular pannus that had caused a partial ankylosis of the joint.