The radiographic and necropsy findings in a case of canine diffuse idiopathic skeletal hyperostosis are reported. Radiographically, the disease was characterized by progressive development of para-articular mineral densities along joint surfaces of the appendicular skeleton; progressive osseous fusion of the ilium, pubis, femur, and ischium; and progressive flowing ossification of the dorsal spinous processes of cervical and thoracic vertebrae. The para-articular lesions were considered to develop as a consequence of fibrocartilaginous proliferation followed by endochondral ossification. Progression of the ossification process led to para-articular joint fusion and almost complete ossification of the metaplastic cartilage. A distinguishing feature was the sparing of intra-articular structures.