Brucella ovis infects sheep causing a clinical or subclinical disease that is characterised by genital lesions and reduced fertility in rams, placentitis and abortions in ewes, and increased perinatal mortality in lambs. Brucella ovis is similar to the other Brucella spp. in its morphology, staining properties and cultural characteristics, except that it gives negative reactions to the oxidase and urease tests. Brucella ovis is usually excreted in semen in infected rams. Passive venereal transmission via the ewe appears to be the most frequent route of infection, but ram-to-ram transmission is also very common. Infected ewes may excrete B. ovis in vaginal discharges and milk and, accordingly, ewe-to-ram and lactating ewe-to-lamb transmission could also be determinant mechanisms of infection. The demonstration of genital lesions (unilateral or bilateral epididymitis and orchi-epididymitis) by palpating the testicles of rams may suggest the presence of this infection in a given flock. Vaccines are available. To date, no human cases have been reported, and B. ovis is considered to be non-zoonotic.