A retrospective study of 400 infants requiring umbilical artery catheterization performed from 1969 to 1971 at Indiana University Medical Center and Marion County General Hospital disclosed six cases of associated osteomyelitis. A similar review of approximately 550 cases of umbilical artery catheterization at Harbor General Hospital from 1972 to 1974 revealed an additional case. The causative organism was Staphylococcus aureus in each instance. Mean onset of symptoms following catheter removal was ten days. In all instances osteomyelitis occurred on the side ipsilateral to insertion and distal to the catheter tip. Postulated mechanisms include bacterial contamination of the catheter, thrombus formation, and local hypoxia from partial occlusion of the vessels by a large catheter.