A silent corticotroph adenoma with multiple cysts was found incidentally at autopsy. By immunohistochemistry, most of the adenoma cells contained reactivity for adrenocorticotropic hormone and beta-endorphin; a few cells stained for beta-subunit of luteinizing hormone. The cysts, interspersed within the tumor, were lined by cuboidal epithelium with foci of stratified squamous epithelium. The lining cells contained immunoreactive keratin; some cells were positive for S-100 protein or glial fibrillary acidic protein, and a few cells were also immuno-stained for adrenocorticotropic hormone and beta-endorphin. It is suggested that this tumor may represent a neoplasm of pars intermedia derivation.