We have studied the deposition of calcium salts in the autopsied intestines which have not been described previously as far as we were able to determine. In order to clarify the incidence, predisposing conditions, mineral compositions of the deposited materials and clinical significance of this phenomenon, we examined 76 cases of consecutive autopsied small intestines by von Kossa's staining. Deposited calcium salts were further examined by electron microscopically, energy-dispersive X-ray spectroscope and electron diffraction analysis. Deposition of calcium salts was observed in the small intestines of 13 cases. Among them, 10 cases were accompanied by hypercalcemia. Deposition of calcium salts was mainly observed in smooth muscle cells of the proper muscle layers and ganglion cells of the Auerbach's myenteric plexus. Intestinal calcinosis was frequently accompanied by deposition of calcium salts in the proper muscle layers of esophagus and large intestine, renal tubules and cardiac myocardial cells. Electron microscopically, the calcium salts were identified as needle-shaped crystals and located on the surface of the extracellular- collagen bundles, in the cytoplasm, mitochondria and nucleus of the smooth muscles cells. Energy-dispersive X-ray spectroscope and electron diffraction analysis suggested the deposited calcium salts as hydroxyapatite. Two patients among the six cases with moderate to severe calcium deposition showed clinical manifestation of paralytic ileus. In conclusion, intestinal calcinosis was frequently observed mostly associated with hypercalcemia. Calcium salts of hydroxyapatite were deposited to the smooth muscle cells and the Auerbach's myenteric plexus of the muscular layer. Deposition of calcium salts might occasionally causes the paralytic ileus but clinical significance of this lesion requires further examination.