In 1952, Lightwood and Payne1 described a new clinical entity which they termed idiopathic hypercalcemia. It was characterized by its occurrence before the age of 1 year, by anorexia, vomiting, constipation, hypotonia, and failure to gain. Clinically it resembles a disease previously described by Lightwood,2 infantile renal acidosis, but differs biochemically in that the former has an elevated serum calcium while the latter a hyperchloremic acidosis. Lightwood distinguishes this condition from one described by Fanconi3 in which the children had mental retardation, chronic renal disease, osteosclerosis, increased NPN, hypertension, elevated serum calcium, and death from renal failure. As there have been some cases of intermediate severity between the two, with a course leading to death, there has been some conjecture as to whether these are related syndromes representing the extremes of a broad spectrum. With no intent to state positively that these are unrelated diseases, this article