The application of angiography to renal diseases has at times led to results that are either unique or misleading in their roentgen appearance. If the entire gamut of roentgen studies—intravenous urography, retrograde pyelography, nephrotomography, and arteriography—are available, the correct interpretation of the disease process is many times evident. This may not be the case, however; the kidney can be poorly demonstrated or nonvisualized by intravenous urography and no retrograde pyelogram is obtained. Thus, there is great hope that arteriography will be a diagnostic study. Valuable information is unquestionably obtained from arteriography, even when ultimate surgery is planned. The spread of disease from the kidney is at times unappreciated from the nonarteriographic examinations, and occasionally an occult metastatic lesion within the abdominal area is identified by angiography. Also, with increasing experience the radiologist is more able to interpret accurately the arteriogram when surgery may be contra-indicated. With this as a goal, many angiographic examinations are performed for the investigation of renal masses: cyst-tumor differentiation, and for other kidney diseases, such as pyelonephritis, hydronephrosis, and the like. The present material includes cases, all proved, in which a specific diagnosis was not possible or the diagnosis was erroneous. The collected material, for the most part, represents a four-year experience of the authors. Malignant Neoplasm The area of greatest concern to both radiologist and urologist is the possibility of mistaking a benign process for a malignant one. On the basis of translumbar arteriographic studies of the kidney, many urologists have concluded that angiography is of insufficient value to warrant its hazard, and they recommend surgical exploration for all renal masses (4, 5, 13, 19). It is hoped that, with selective renal artery catheterization and serial filming, this objection may be overcome. The view that all masses must be explored, especially in elderly patients in whom surgery may be medically contraindicated, is as fallacious as the statement that a correct diagnosis can be made in every case. There are indeterminate studies due to suboptimal roentgenograms and atypical appearances (1, 10). Even if we exclude the poor diagnostic studies, there is still a small group of cancers, particularly the tubular and papillary adenocarcinomas, that can mimic a benign cyst. Tubular and Papillary Adenocarcinoma: The tubular and papillary adenocarcinomas (Fig. 1) have a poor blood supply but are not necrotic. The arteriogram shows an interface between the normal kidney and the tumor that simulates a cyst. Contrast “puddling” is absent in the mass during the nephrogram. The two cases in our experience had the angiographic findings of a simple cyst. Nephrotomography might have shown a thick wall about the neoplasm but was not performed.