The authors report six cases of milk of calcium syndrome. As in previously published cases, the diagnosis was established by the film taken in the standing position: the "lithiasic density" shrinks, densifies and exhibits a horizontal upper edge. Four patients were at first mistakenly diagnosed as having urinary lithiasis for which extracorporeal lithotripsy was scheduled. In one case, the lithotripsy was actually performed and the diagnosis of milk of calcium disease was established only immediately after the procedure. In another patient, lithotripsy was performed because small stones were thought to be present in the milk of calcium. In the two other cases, the diagnosis was made on the day before scheduled lithotripsy and this procedure was therefore cancelled. The purpose of the authors in reporting these cases is above all to point out the diagnostic value of a plain film of the abdomen in the standing position. Diagnosis must be made in time to avoid extracorporeal lithotripsy since, in milk of calcium syndrome, this procedure is illogical, inefficient and probably more hazardous than useful. On the basis of the six cases reported herein and of data from the literature, several characteristics of milk of calcium syndrome can be emphasized. Milk of calcium syndrome predominantly affects individuals with a positive personal or family history for renal lithiasis. It occurs in both sexes and all age groups, including childhood. Milk of calcium syndrome complicates partial or total dilatation of the urinary tract. Crystallization may be of the phosphatic or oxalic type. Concomitant urinary tract infection is common.(ABSTRACT TRUNCATED AT 250 WORDS)