A large tumor of the left lateral ventricle in a 3 1/2 year old male was diagnostic of malignant choroid plexus papilloma (choroid plexus carcinoma) as observed histologically. Focal neoplastic epithelial cells contained yellow-brown pigment which was not entirely compatible with melanin by histochemical techniques. Ultrastructurally, the tumor had definite evidence of choroid plexus origin. The neoplastic cells contained electron-dense and lamellar bodies, as well as structures of intermediate type. Premelanosomes were not observed. Thus there was no evidence for neural crest melanin. It is suggested that the pigment is probably lipofuscin and melanin derived from lipofuscin by “melanization” through pseudoperoxidation.