Common primary midline brain tumors can be adequately diagnosed by cytologic methods if their results are interpreted in the light of the clinical setting and the neuroradiologic findings. The type of cytologic material appropriate for diagnosis will vary with the type of lesion. Cerebrospinal fluid (CSF) cytology is considered useful for the diagnosis of malignant teratomatous lesions, which frequently include an abundant germinomatous (seminomatous) element since these tumors readily exfoliate into the CSF. In other common lesions (craniopharyngiomas and pituitary adenomas), direct aspiration methods are thought to be more applicable. Aspiration cytology was unable to provide a definitive diagnosis in two midline cystic lesions, both apparently benign, and it is suggested that the method may have certain drawbacks in differentiating such lesions. Nerve tissue neoplasms, which not infrequently arise in the midline structures, were not included in this series.