Fractures of the posterior ribs are well-recognized sequelae of infant abuse. Previous reports have indicated a predilection for fracture near the costotransverse process. This study expands the spectrum to include fractures involving the rib head. The radiologic and histologic features are described, and the mechanism of injury of this lesion is examined. In situ and specimen radiography, followed by histopathologic examination, was performed in 78 ribs removed from seven abused infants who died with posterior rib fractures. Computed tomography of the intact posterior thorax was performed in two of these infants. Fifty posterior rib fractures were identified; 29 involved the rib head. Frontal radiography was insensitive in identifying these fractures, clearly revealing injury only when periosteal reaction was present (four of 29 cases). Axial specimen radiography delineated the fractures in all cases. In the two infants studied, CT depicted five of 19 fractures visible only with axial specimen radiography. The morphologic features of these fractures further support the concept that most fractures in abused infants occur by means of indirect forces and are consistent with anteroposterior manual thoracic compression during assaults.