Pituitary dwarfism is a genetically heterogeneous group of disorders associated with a variety of pathogenetic mechanisms which may involve any level of the hypothalamic-pituitary-somatomedin-peripheral tissue axis. Developmental defects of the pituitary, such as congenital absence of the pituitary, and developmental defects of the hypothalamus, such as anencephaly and holoprosencephaly, have been described. Degeneration of the hypothalamus and pituitary, as in histiocytosis X, may also result in pituitary dwarfism. In "idiopathic" forms of pituitary dwarfism, defects limited to either the hypothalamus or pituitary have been suggested by releasing hormone stimulation studies and it is quite likely that specific defects of the hypothalamus, and pituitary, as well as defects in releasing hormonal synthesis and secretion and growth hormone synthesis and secretion all exist. In Laron dwarfism the basic defect appears to lie in the ability to generate somatomedin, in the Pygmy the defect appears to involve peripheral unresponsiveness to somatomedin. Further pathologic studies of the hypothalamus and pituitary in pituitary dwarfism; analysis of growth hormone and somatomedin cellular receptors; and elucidation of the structure of growth hormone releasing factor and techniques for its synthesis and assay should allow for the delineation of the specific pathogenetic mechanism in each of these syndromes.