Sarcoidosis is a multisystem disorder of unknown etiology that frequently involves the lymph nodes, lungs, eyes, and skin. The disease can involve any organ system, and noncaseating granulomas are characteristically present. Synthesis of 1,25-dihydroxyvitamin D, the most biologically active form of vitamin D, occurs in granulomatous tissue and may give rise to increases in its concentration in the peripheral circulation and to hypercalcemia and hypercalciuria. Infiltration of endocrine organs also occurs. Involvement of the hypothalamus and pituitary can cause primary polydipsia and disordered regulation of thirst; diabetes insipidus, impaired secretion of anterior pituitary hormones (with clinically apparent hypothyroidism, hypogonadism, hypoadrenalism, or impaired growth), and increases in serum prolactin may also result. Galactorrhea, however, seldom occurs. Involvement of the thyroid and adrenal glands rarely leads to hypofunction. Involvement of the pancreas rarely occurs but does not produce diabetes mellitus. Involvement of the male reproductive system results in epididymitis and hypogonadism, and involvement of the uterus causes abnormalities in menstrual function.