The objective of the study was to develop a simple clinical tool to identify serious bacterial infection (SBI) in children with fever without a source. For each child, a clinical assessment, a white blood cell count, a urine analysis, a determination of C-reactive protein, procalcitonin, and appropriate cultures were performed. Two hundred two children were studied of whom 54 (27%) had SBI. In the multivariate analysis, only procalcitonin [odds ratio (OR): 37.6], C-reactive protein (OR: 7.8), and urine dipstick (OR: 23.2) remained significantly associated with SBI. The sensitivity of the score for the identification of SBI was 94% and the specificity 81%. In the validation set the sensitivity of the score was 94% and the specificity 78%.