Four cases of cystic meningiomas were found among 194 meningiomas diagnosed by computed tomography (CT) and operated on during a 7 year period, an incidence of 2%. The cysts were in all cases peritumoral. The cyst's wall was the brain itself, and the ependymal ventricular wall was part of their medial boundary. They contained xanthochromic fluid with a high protein content. Three meningiomas were parasagittal and one was adjacent to the pteryon and the external part of the sphenoid ridge. The mural nodules were in 2 cases apparent single nodes although in one it was part of multiple distant and regional growths, in another the tumour was built by the aggregation of 2 nodes, the remaining case was an "en plaque" meningioma. All were definitely attached to the dura. Histological pattern was different in every case. Those parasagittal were: one pure meningotheliomatous, one mixed meningotheliomatous with pseudo psammomatous and lipoblastic sections and one highly vascular angioblastic; the pteryonal case was psammomatous and microcystic. CT diagnosis is difficult because glial, metastatic and other tumours may look cystic and resemble cystic meningiomas. Nevertheless in 3 cases the correct diagnosis was suspected preoperatively because the solid portion of the tumour showed intense and homogeneous contrast enhancement with a sharp edge and was located adjacent to the dura. On the other hand in the remaining case, the parasagittal solid tumour was not readily apparent on CT (the "en plaque", case), and the tentative preoperative diagnosis was of an epidermoid tumour.(ABSTRACT TRUNCATED AT 250 WORDS)