Most infections of the upper urinary tract are straightforward and do not require any emergency radiological investigations. A sonogram carried out within 48 hours will in most cases be sufficient to eliminate obstructed pyelonephritis requiring emergency drainage of urine. In complicated cases, or those affecting already weakened areas, an urgent CT scan is necessary, preferably after injection of iodinated contrast medium if renal function permits. CT scanning is far better at diagnosis than sonography as well as at investigating whether there are complications. Furthermore, it is essential that the radiologist is aware of unusual and rare forms of pyelonephritis, especially pseudotumoural forms, so that clinicians can be pointed towards the appropriate treatment, avoiding unnecessary and invasive interventions.