A case of tubular adenoma arising in the right ventricular choroid plexus of a 4-month-old boy is described. A basic pattern of neoplastic glandular epithelium and lack of papillary architecture distinguished this tumor from a papilloma. Coexpression of S -100 protein, transthyretin and cytokeratin identified the neoplastic cells as being of choroid plexus origin. Immunohistochemical detection of MIB-1 showed a proliferation rate (16%) similar to adenomas in more conventional locations, but not encountered in benign brain tumors. In situ detection of DNA-derived oligonucleosomal fragments by TUNEL analysis, on the other hand, detected apoptotic activity in 5-8% of tumor cells. The indolent course of the disease in the present case, thus, might suggest a compensatory elimination of proliferating cells by apoptosis. This possibly points to mechanisms of neoplastic transformation different from those involved in choroid plexus papillomas.