Pyelonephritis is a bacterial infection of the upper urinary tract and renal parenchyma. Infection occurs primarily by urinary contamination upward and backward from the intestinal flora, and genital skin, explaining that the seeds are most commonly encountered Gram-Negative bacilli (GNB), Escherichia coli in mind. The peak incidence is among women aged 15 to 65, but pyelonephritis may include subjects of all ages and both sexes. The diagnosis is usually straightforward and based on a combination of fever, unilateral flank pain and a positive urine culture. Biology and imaging aim to seek any form of pyelonephritis complicated, especially due to the obstructive form a barrier (usually a calculation) of the urinary tract and is a surgical emergency. Support depends on the existence of signs of severity or complications. Treatment consists of antibiotics, to begin immediately, initially probabilistic and secondarily adapted to the antibiogram. Patients hospitalized in the urology will be those with complicated pyelonephritis (urinary obstruction, abscess, sepsis, renal insufficiency, solitary kidney, comorbidity).