82 febrile young infants were studied, prospectively, at the Emergency Service in Hospital Universitário - University of São Paulo. All the children were kept at the Emergency ward for 24 hours. Clinical and laboratory investigations were performed and when necessary, administration of antibiotic agents were started. 18 infants exhibited potentially severe bacterial infections (21.9%). Several important disorders were recognized in 40 infants (48.8%). All infants were followed until the end of the febrile episode: 20 children as inpatients and 62 as outpatients. 38 infants received antibiotic therapy (46.3%). Evolution was satisfactory in all patients. The authors detected in young febrile infants potentially dangerous clinical conditions that need close observation, laboratorial investigation and frequently antimicrobial therapy. The observation period at the Emergency ward was important to allow these procedures and to decide about hospitalization need.