Our purpose was to document the incidence and imaging features of cystic meningiomas, to correlate the imaging features of cystic meningiomas with the histopathological findings, and to analyze the surgical implications of the imaging features of cystic meningiomas. The imaging studies, clinical histories, operative findings, and histopathological findings of a total of 128 patients with meningiomas were reviewed retrospectively. The 15 cystic meningiomas in our series could be morphologically divided into three major types: cystic areas contained wholly within the tumor (6 meningiomas), cystic areas at the periphery of, but wholly within, the margins of the tumor (5 meningiomas), and cystic areas peripheral to the tumor, lying on the adjacent brain (4 meningiomas). A majority of cystic meningiomas were histopathologically diagnosed to be meningothelial (8 of 15 meningiomas). Cellular atypia was seen in many patients. Meningiomas may simulate astrocytomas or metastatic lesions on imaging studies. Magnetic resonance imaging had a diagnostic accuracy of 80% (12 of 15 patients), which was significantly better than the computed tomography diagnostic accuracy of 50% or less. Magnetic resonance imaging with contrast enhancement could distinguish Type 2 (cyst wall containing tumor cells) and Type 3 (cyst wall containing gliotic tissue without tumor invasion) cystic meningiomas. Cyst wall enhancement was seen in Type 2, but not in Type 3, cystic meningiomas. Cystic meningiomas represented approximately 10% of all meningiomas in our series. Histiologically, they were usually relatively aggressive, which probably partly explains why cystic changes may be secondary to tumor necrosis or hemorrhage. Recognition of the diagnostic features of cystic meningiomas is important, because they may mimic metastatic neoplasms or primary gliomas.(ABSTRACT TRUNCATED AT 250 WORDS)