A study of 111 cases of cranial cruciate ligament disease, seen over a three year period has been made. Fifty-five of these dogs were under four years of age (average age 21.4 months) and most were of the larger breeds, particularly the rottweiler (25 per cent). The onset of clinical signs was sudden in 53 per cent and gradual in 47 per cent of these cases; bilateral disease was present in 31 per cent. The severity of the lameness was variable. The pathogenesis of the disease appears to involve a gradual stretching, partial rupture and eventually a complete rupture of the cranial cruciate ligament. The term cruciate disease has been used to cover this spectrum of ligament pathology and the clinical signs can appear at any stage during this ligament degeneration. Slight anterior drawer movement can often be detected during the earlier stages of stretching and partial rupture but this can only be appreciated under general anaesthesia. Osteoarthritis is initiated during the early stages and may be well established by the time the cruciate completely tears. The predisposition to cruciate disease in these young dogs of the larger breeds is difficult to explain but may be related to inadequate exercise during puppyhood.