Seven cases of retroperitoneal neurilemoma confirmed by histology had an ultrasound examination. There were 5 women and 2 men with a mean age of 55. Most of the cases (5/7) had a palpable mass clinically. Of the 7 cases, 4 had a mass with cystic degeneration and internal echoes on sonogram, consistent with the macroscopic findings of tumors. The internal echoes represented blood clots and residual tissue (or septa) in cyst. Of the remaining 3 cases, one showed a confluent lobulated mass, the second had a solitary homogeneous mass with small cysts, and the third one, which was the smallest (4 cm x 4 cm x 6 cm), had a hypoechoic and homogeneous pattern. The sonograms of all 7 cases were consistent with the macroscopic features of the tumors. The sonographic pattern of tumor parenchyma is either homogenously hyperechoic or hypoechoic. Because of the cystic degeneration, hemorrhage, and residual tissue of retroperitoneal neurilemoma, the sonographic pattern was variable.