The utility of computed tomography (CT) in evaluation of the retroperitoneum was assessed in 54 pediatric patients and compared with that of conventional radiography. In 20 patients (group 1) with an abnormality on conventional radiographs, CT improved diagnostic understanding in 17 and affected management in four patients. In 31 patients (group 2) with clinical suspicion of a mass but normal abdominal radiographs, CT contributed diagnostic information in seven and had a beneficial effect on therapy in five patients. CT contributed diagnostic information in three other patients evaluated for trauma (group 3). CT was most useful in defining the extent of a lesion in group 1 and in demonstrating absence of a suspected mass in group 2.