Patients (33) with cystic intracranial lesions were examined with both magnetic resonance (MR) imaging and CT [computed tomography] scanning. The abnormalities imaged included 11 arachnoid cysts, 10 cystic tumors, 6 postoperative cysts, and 3 colloid cysts. The intensity patterns of the cyst contents as encoded with routine spin-echo imaging sequences enabled subdivision of the cysts into 3 categories. Arachnoid and postoperative cyts had intensity pattern identical to CSF. More proteinaceous cysts, inlcuding inflammatory cysts and nonhemorrhagic tumoral cysts, had an intermediate intensity pattern with characteristically low intensity on the short TR sequence (0.5 s), but had clearly higher intensity than cerebrospinal fluid on the long TR sequences (2 s). Finally, 3 cystic tumors with hemorrhagic fluid and 3 colloid cysts had a distinctly different pattern of high intensity on all 4 MR sequences through the same section. MR was superior to CT in characterizing intracranial cystic lesions because of its ability to categorize cysts into these 3 groups on the basis of the intensity pattern of cyst contents, thereby improving diagnostic specificity and patient management.