A congenital syndrome of long, thin limbs, severe joint and tendon laxity, microspherophakia, ectopia lentis, heart murmurs and aortic dilatation was identified in 7 calves. All affected calves were sired by a single phenotypically normal bull suspected of germline mosaicism for a new mutation resulting in this disease. One of the calves subsequently died with ruptured aorta at age 16 months. Histopathologic and electron microscopic studies of the aortic media of affected calves demonstrated disorganized elastin and narrowed elastic lamina separated by widened spaces. This bovine disease provides a unique animal model of the human Marfan syndrome. A herd of cattle with this disease is being developed for further studies.