An unusual tumor of the pituitary gland is reported. The most characteristic finding of the present tumor was the presence of numerous "colloid" and mucoid secretions. The cells were stellate in shape and there were intra- or intercellular lumina which were lined by many microvilli and occasional cilia. There were also large accumulations of 10 nm filaments in their cytoplasm. Junctional devices were well formed at the points of mutual contact of these cells. They thus correspond to fetal follicular cells of the anterior pituitary lobe. For this reason, "folliculo-stellate cell adenoma of the pituitary" would best characterize this hitherto undescribed neoplasm.