There is an ongoing debate on the best way to screen febrile infants for urinary tract infection. We examined the urinanalysis (UA) findings on admission among infants less than 16 weeks old, with and without acute pyelonephritis (APN), as defined by the dimercaptosuccinic acid (DMSA) renal scan findings, performed during a 57-month period. Forty-nine cases with a positive DMSA scan were compared with 79 negative study cases. A negative UA for leukocytes (< 5 white blood cells/high power field) was found in 4 of 49 (8.1%) cases with APN by DMSA, and in 34 of 79 (43%) cases with a negative DMSA (odds ratio 10.88 (95% confidence interval, 2.31 to 70.3; P < 0.001)). Three of the 4 infants not suspected to have APN by their UA findings would have been admitted for a full sepsis workup based on their clinical presentation and/or their laboratory findings on admission. We conclude that a fresh UA may be a sufficient screening method for the exclusion of APN in infants assessed for fever of no obvious origin.