Extravasation of the contrast medium during the course of retrograde pyelography is not rare. If the material is forcibly injected, thereby raising the intrapelvic pressure above a critical level, any or all of various backflow phenomena may result. In addition to the backflow patterns, actual traumatic rupture of calyx, pelvis, or ureter by the catheter may occur. During intravenous pyelography, on the other hand, extravasation has rarely been described. The phenomenon is not likely in the course of a procedure which is essentially one of physiologic secretion. Certain aspects of the examination as it is usually performed may, however, simulate the conditions of increased intrapelvic pressure, which occurs so frequently in retrograde pyelography. Hendriock (1) was the first to note pyelorenal reflux in excretory urography. He suggested that this could lead to the spread of infection from pelvis or ureter into the renal parenchyma. No compression was used in his case, but the patient experienced colic and, therefore, quite possibly spasm resulting in increased intrapelvic pressure. A case of pyelolymphatic backflow during intravenous pyelography was reported by Narath (2), but here again no external compression was used. Thus the author's assumption that intravenous urography is simply a matter of physiologic excretion, while true in 1938, would not necessarily hold today, when external compression is commonly employed. Following the introduction of external compression as an accepted technic in intravenous pyelography, Coliez (3) classified the types of extravasation which might occur. He referred to Puigvert Gorro's statement that intra pelvic pressure is increased in the presence of an acute ureteral obstruction, calculus, kink, or spasm, and even in certain subacute obstructions. Coliez described an interstitial type of extravasation which, in extreme cases, would invade the cortex and cause subcapsular extravasation on the convex side of the kidney or pass through the renal sinuses to the hilus and then into the subcapsular space. Although the latter situation has been postulated, no actual report has appeared in the literature. The present case is believed to be the first reported example of subcapsular reflux occurring secondary to rupture of the renal sinuses. Case Report A 48-year-old white woman was admitted to St. Luke's Hospital complaining only of mild gastrointestinal symptoms and hypersensitivity to the common allergens. Physical examination was essentially negative, except for absence of the right breast, which had been removed five years previously for carcinoma. Intravenous urography was performed as a part of a general work-up. A preliminary film of the abdomen was negative. There was normal visualization of both renal collecting systems five minutes after intravenous administration of contrast material (Fig. 1).