Spontaneous renal extravasation is the term used to refer to the radiological demonstration of contrast medium outside the collecting system without previous trauma, ureter catheterization, operation on the kidney or its vicinity, and without external compression during urography. In a review of 1300 intravenous urograms, 13 cases of extravasation of contrast medium were found to satisfy the above criteria. Differences in the radiological appearance may cause problems with regard to evaluation and classification. From a therapeutic point of view it is important to distinguish between two forms: transient sinus extravasation due to minute tears in the calyceal fornix after an increase in intrapelvic pressure and persisting rupture of the previously impaired renal pelvis, which may require surgical intervention.