Many cases of enteroliths were reported in the nineteenth century but the number greatly decreased in the early twentieth century. However, in recent years the number of cases in certain parts of the United States such as California has greatly increased. The reasons for the increase are obscure. The intake of nitrogen, magnesium and phosphorus (the primary components of enteroliths) from water and food is likely to be a factor. Arabians may be more likely to develop enteroliths than horses of other breeds. A nidus such as a small stone is needed because a nidus has been found in every enterolith that has been examined. Further studies in which the effect of mineral intake and form of the mineral on enterolith formation are needed. Studies of enterolith formation in the past have all been retrospective. Models for the development of enteroliths are needed.