Abstract Introduction: Fever continues to be the most frequent cause of care in the pediatric population. It is frequently the use of invasive and unnecessary tests which results in discomfort to the patients. The present study aims to describe the epidemiology of urinary tract infection (UTI) in children with fever without source aged 0–36 months and to evaluate if there are differences in the magnitude and days with fever in patients with and without urinary tract infection and fever without focus.MethodsWe included children aged 0–36 months presenting with fever without source in our emergency unit. Demographic and clinical characteristics, investigations, and management procedures were recorded at the time of inclusion. Potential predictors of SBI-UTI were compared between patients with and without SBI-UTI.ResultsBetween January 2015 to December 2017, 137 patients were included. Forty children (29.2%, CI 95% 21-36%) were diagnosed with SBI. A total of 32 children (43%) had a final diagnosis of SBI, which were all urinary tract infections (UTI). There were no differences statistically significantly between the groups in appearance in admission, magnitude and days with fever, white blood cell count, CPR levels.ConclusionsIn patients with FWS under 3 years of age, urinary tract infection is the main cause of SBI. A high degree of clinical suspicion should be maintained since neither symptoms, signs, CBC or CPR distinguish children with or without UTI in this population. Future studies should further validate, in a different setting and in a larger population, our results.