Bilateral spontaneous osteoarthritis of the stifle joint was observed to cause progressive lameness in 3 Holstein-Friesian and 52 Jersey cows 5–13 years old. Both breeds were represented by one herd each, and no affected males were ascertained in either herd. Pedigree information in case of the Holstein-Friesians and maximum likelihood proportions of arthritics in maternal halfsib families in case of the Jerseys suggest inheritance of the disease in dairy cows by means of a single pair of autosomal recessive genes. Penetrance is very low, mainly because of the variable and late age of onset. The literature concerning genetic aspects of the disease in mammals is reviewed.