Milk-of-calcium renal stone was first described by Howell in 1959 (2), and subsequently 3 additional cases have been reported in the world literature (1,3, 4).2 This stone, which is a suspension of calcium carbonate in a renal cyst or calyceal diverticulum (4), is similar to the milk-of-calcium bile deposited in the biliary tree. Why the material does not solidify into the usual type of renal or biliary calculus is not known. The suspension is heavier than urine or bile and therefore layers in the most dependent portion of a calyceal diverticulum or renal cyst. Howell and Walker et al. (4) emphasized the importance of the calcium suspension assuming a fluid level in the diagnosis of this condition. Howell's case, however, was originally thought to be one of solitary renal calculus. Correct diagnosis followed study of postoperative films after the surgeon had failed to locate the stone. Report of a Case A 56-year-old white male with a twenty-year history of recurrent peptic ulcer was admitted to Wilford Hall USAF Hospital with acute abdominal pain in December 1963. In 1957 a duodenal perforation had been treated with primary closure; a calcific density observed on roentgenograms at that time was interpreted as being situated in the liver. On the present admission the ulcer disease was exacerbated, and the diagnosis was acute gastric obstruction secondary to chronic pyloric stenosis. Roentgenographic studies again demonstrated a density in the right upper quadrant of the abdomen (Fig. 1). Oral cholecystograms revealed no abnormalities. Excretory urography with oblique and upright films showed the density in the upper pole of the right kidney (Figs. 2 and 3). Discussion and Summary Milk-of-calcium stone, though rare, may occur within a renal cyst (1) or a calyceal diverticulum (2, 4). A fifth case is presented. As demonstrated in this instance, and also in that of Pullman and King, the presence of milk of calcium in the biliary system must be excluded. The importance of recumbent and upright radiographs in the diagnosis of the condition has been emphasized (1, 4).