Four patients with brain tumors were diagnosed with atypical teratoid/rhabdoid tumors and underwent CT and MR imaging. For all tumors, aggressive features were shown by imaging studies and included hydrocephalus, apparent invasion of the adjacent brain and dura, and marked mass effect. The striking heterogeneity of the atypical teratoid/rhabdoid tumor shown by imaging studies reflects the histopathologic complexity of these tumors, and awareness of atypical teratoid/rhabdoid tumor is important in making the correct diagnosis of this uncommon but probably underdiagnosed entity.