Castleman disease is a relatively rare disorder affecting young adults. We present the CT and ultrasonographic findings of Castleman disease in two children. In one patient with hyaline-vascular type disease, CT showed a well-enhancing mass in the right paratracheal area. In a second patient with plasma cell type disease, there was a solid, homogeneous mass in the retroperitoneal space which was poorly enhancing. Ultrasound showed a uniform hypoechogenic mass in both cases.