Endocrine disorders occur because of hypersecretion, hyposecretion, or nonresponsiveness by target cells. Hypersecretion is usually due to secreting tumors, autoimmune disease, or excessive stimulation of the gland by trophic signals. Hyposecretion may be due to failure or congenital absence of glandular tissue, autoimmune destruction, surgical removal of the gland, or lack of normal trophic signals. Hyporesponsiveness is clinically similar to hyposecretion and is due to hormone receptor dysfunction. Endocrine disorders involving the hypothalamic-pituitary system are often classified as primary or secondary. Primary endocrine disorders result from intrinsic defects within the hormone-secreting gland. Secondary disorders result from abnormal pituitary secretion of trophic signals. Manifestations of an endocrine disorder are due to abnormal target gland function and are therefore similar whether the etiologic classification is primary or secondary. Hyposecretion of gh results in decreased linear growth in children. In some cases decreased linear growth occurs despite normal gh levels, and abnormalities of igf-1 generation or responsiveness are suspected.