Identifying acute pyelonephritis (APN) with early obstructive uropathy is clinically important in the emergency department (ED) because obstructive urolithiasis is an independent risk factor for inpatient death, prolonged hospitalization, and failure of outpatient APN therapy. Furthermore, diagnosis of an early obstructive uropathy can be difficult when based solely on clinical findings. Clinicians may assume the cause of the patient's symptoms to be APN alone, without considering the concurrent presence of an obstructing stone. A feasible screening test to detect early obstructive uropathy in cases of APN has not been previously identified. Plain film radiographs are insensitive in locating a suspected calcified stone. Computed tomography is readily available in most EDs and clearly defines urologic anatomy, but delivers unnecessary ionizing radiation, can prolong ED length of stay, and is not cost-effective as a screening test for all patients diagnosed with APN. We report a case in which a bedside ultrasound identifying hydronephrosis prompted confirmatory computed tomography imaging and emergency consultation of a patient with APN. In this case, hydronephrosis on bedside ultrasound examination was an indirect marker of a distal ureteral obstruction. By detecting the presence of hydronephrosis in patients with APN, emergency physicians may dramatically increase their ability to identify those patients that need further radiographic investigation and ultimately decrease the rate of outpatient treatment failure. Further surveillance data are needed to determine the statistical characteristics of this novel screening test and if routine renal evaluation of all patients with APN is warranted.