Three aneurysmal bone cysts of the rib in infants are presented. These tumors were engrafted on vascular and cartilaginous hamartomas and thus showed the unusual feature of hyalin cartilage associated with aneurysmal bone cyst. The entity of vascular and cartilaginous rib hamartoma is discussed with emphasis on the importance of distinguishing this malformation from a benign or malignant neoplasm.