PURPOSE: To evaluate radiologic findnings of rhabodmyosarcoma of children in the head and neck concerning theorigin, morphologic characteristics, extent, and the route of intracranial extension on CT and MR. MATERIALS AND METHODS: Twenty cases of pathologically proven rhabdomyosarcoma were analyzed. Fifteen CT scans (postcontrast CT(n=13), precontrast CT (n=2)) and eleven MR scans were obtained. Postcontrast MR scans were performed in the tencases. Six cases had CT and MR scans. Nine cases had only CT scan and five had only MR scans. We retrospectivelyanalyzed the origin, morphologic characteristics (attenuation, signal intensity, margin), extent, intracranialextension, route and clinical staging of rhabdomyosarcoma on CT and MR scans. RESULTS: Out of the twentyrhabdomyosarcomas, sixteen cases were of parameningeal group. Ten cases of parameningeal group located in theinfratemporal fossa which was the most common site of origin. The mass showed iso-density in the 8 cases (62%) andhigh density in the 5 cases (38%) on the postcontrast CT scans compared with the muscle. All cases on the CT scanshowed homogenous attenuation of the tumor except one which showed internal necrosis. Twelve cases (80%) on preandpostcontrast CT scans (n=15) showed moderately-defined margin and the rest showed ill-defined margin. On MR scans,all the cases (n=11) showed iso- and high signal intensity on T1WI and T2WI, respectively. Strong enhancement ofthe mass was seen in all cases (n=10). Nine cases showed homogenous signal intensity of tumor on pre-andpostcontrast MR scan while 2 cases showed inhomogenous signanl intenisty because of hemorrhage(n=1) andnecrosis(n=1). Therefore the margin of rhabdomysarcoma on all pre-and postcontrast MR scans was well-defined. Theextent of rhabdomyosarcoma was various depending on corresponding origin and parameningeal group showed widerextent than other head and neck group. Infratemporal rhabdomyosarcoma showed expansile growth and intracranialextension via foramen ovale. Those in the middle ear invaded intracranium by directly destoying petrous bone andvia internal auditory canal. Those in the nasal cavity extended into intracranium by directly destroying skullbase of frontal lobe. Nasopharyngeal one extended into intracranium mainly by directly destroying base of skull orpartially via foramen ovale. Clinical Stage 1,2 and 3 were one, four and fifteen cases, respectively. CONCLUSION: Rhabdomyosarcoma of children in the head and neck tends to show relatively severe bony destruction of skull baseand various intracranial extension routes can be helpful radiologic findings on the CT or MR scan although its CTdensity or signal intensity of MR was not specific. And it is peculiar that infratempral fossa was the most commonsite of origin of rhabdomyosarcoma.