Actinomycosis is a rare, deep-seated infection of the jaw of cattle that include the progressive enlargement of bone structures. It is caused by Actinomyces bovis, a gram-positive rod found as a normal commensal of the alimentary canal in otherwise healthy animals. This paper shortly describes Actinomyces bovis and its ability to cause "lumpy jaw" or actinomycosis in cattle. It will describe its pathogenesis, diagnosis, treatment and some clinical presentations. The incidence of symptomatic actinomycosis infection is quite low in Sweden today.