A condition has been recognised in five young dogs in which the proximal tibia exhibited cranial bowing. This altered conformation, sometimes accompanied by bow legs (genu varum), occurs bilaterally, but to differing degrees. The deformity apparently altered the biomechanics of the stifle joint so that degenerative joint disease and rupture of the cranial cruciate ligament followed in four of the five dogs. The aetiology is unknown, but the most likely cause appears to be retardation of growth in the caudal aspect of the proximal tibial physis. Treatment involving surgical techniques to correct the joint instability was only moderately successful.