Four hundred and forty-five bovines with bone infection of the appendicular skeleton were selected for clinical and radiographic assessment. A distinction was made between hematogenous and posttraumatic origin (wound/fracture). Bone infection was classified into four types according to the site of infection: type 1 is metaphyseal and/or epiphyseal osteomyelitis close to the growth plate; type 2 is primary subchondral osteomyelitis mostly accompanied by septic arthritis; type 3 is infectious osteoarthritis with subchondral osteomyelitis implicating that infection in the subchondral bone originates from the infection. Type 4 summarizes bone infections which can not be categorized in the previous groups. Hematogenous osteomyelitis is 3.2 times more frequent than post-traumatic osteomyelitis. Within the different groups, the relation of hematogenous to post-traumatic infection changed significantly. In type 1 infection the ratio was 5/1, in type 2 the ratio was 8/1 and in type 3 it was 3/1. Epiphyseal or metaphyseal osteomyelitis exhibited early radiographic bone changes, whereas with infection emihating from the joint, the bone lesions were detected later, because the bone was infected as a consequence of a primary septic arthritis. In smaller bones, severe and complete bone destruction was often present. Hematogenous bone infection never involved the entire diaphysis. Actinomyces pyogenes was discovered to be the main etiologic agent, whether or not combined with anaerobes. Bone fragments from the metaphysis of young calves were subjected to the effect of pure cultures of different bacteria. Radiographic changes to the structure of the bone were not identified within 2 weeks. Rapid radiographic changes in osteomyelitis cannot be explained by the direct effect of the bacteria on bone tissue in vivo. General infections of the lungs, disorders of the intestines and other internal organs were rarely responsible for osteomyelitis or septic arthritis. Osteomyelitis and infectious osteoarthritis is probably often induced by external and internal traumatic events to joints and bones in cattle.