To evaluate inhibin-A immunoreactivity and its utility in the differential diagnosis of nervous system neoplasms and non-neoplastic lesions. An immunohistochemical study of 252 central and peripheral nervous system tumors and 40 nonneoplastic lesions was undertaken. Brain lesions included the basic spectrum of astrocytic, oligodendroglial, and ependymal neoplasms, as well as glioneuronal, pineal parenchymal, choroid plexus, and embryonal. Meningeal neoplasms, basic peripheral nerve tumors, and uncommon sellar lesions were also assessed. Non-neoplastic lesions included demyelinating disease, progressive multifocal leukoencephalopathy, organizing infarct, and reactive gliosis. Diffuse cytoplasmic, membranous, and perinuclear cytoplasmic staining patterns were observed. Significant immunoreactivity was noted in glioblastoma (12 of 20), pleomorphic xanthoastrocytoma (6 of 10), ganglioglioma (8 of 10), meningioma (14 of 20), and hemangioblastoma (10 of 10). Peripheral nerve and sellar tumors as well as non-neoplastic lesions were entirely immunonegative. In our study that investigated the inhibin-A immunoreactivity in a broad spectrum of nervous system lesions, inhibin-A positivity was established in various low-grade and high-grade central nervous system tumors. Thus, inhibin-A is not a specific marker of hemangioblastoma and may be of limited utility in the differential diagnosis of astrocytic and meningothelial neoplasms. Its pathophysiologic role in these various tumors remains to be determined. Further evaluation of the possible significance of staining patterns and degrees of reactivity relative to pathobiology and/or prognosis significance is required.