With advancing years a dog may suffer from a variety of conditions of its musculoskeletal system which adversely affect its ability to exercise and may cause it to be retired from activities in work and sport for which it has been trained. Arthritis is common, and in many cases arises from developmental errors suffered in puppyhood, such as hip dysplasia, osteochondrosis and growth plate disorders. Trauma to joints (ligament ruptures, dislocations and fractures) may also be the precursor of degenerative joint changes later in life. It is important, therefore, for all such conditions to be corrected as effectively as possible if joint disease is to be minimised as the dog grows older. Preventive action is also required for some conditions for which correction may not be entirely feasible, so the identification of modes of inheritance is important if those are to be controlled by breeding. Certain spinal disorders also tend to increase in prevalence with age, particularly spondylosis deformans, neoplasms and chronic degenerative radiculomyelopathy. As it happens, spondylosis in mild to moderate degree affects pet dogs very little, but a reduction in spinal flexibility can cause problems for dogs required to be agile in work or sport. In common with other body tissues, neoplasm of the locomotor system increases in occurrence in older dogs, and although the overall incidence of tumours of bones, joints, nervous tissue and muscle is relatively low, these are the most serious of all the limb and spinal conditions encountered because of their life threatening propensities. The treatment required covers a wide range from simple changes of management in order to reduce exercise, to the use of analgesics and anti-inflammatory drugs and to surgery to remove diseased tissue, stabilise joints or reduce pain with forms of arthroplasty or arthrodesis.