Objective: To describe the clinical and epidemiological profile of acute respiratory infections (ARI) in children younger than five years old, of both sexes, diagnosed at the University Hospital Júlio Müller.Methods: This is a descriptive and cross sectional study. A standard questionnaire was answered by the children's parents, during the period of October/1996 to February/1997. The cases were classified according to the Health Ministry criteria in Upper Airway Infection (UAI) or Acute Lower Respiratory Infection (ALRI). The following data were analyzed: signs and symptoms, clinical diagnosis, socioeconomic variables, nutritional appraisal and passive smoking. The data were analyzed with EPI-Info 6.02b program. The c 2 test was used with confidence interval of 95% (a = 5%).Results: The ARI prevalence in children under five years was 25.6%. From the total number of 491 children, 76.4% (n=375) had UAI and 23.6% (n=116) ALRI. The most frequent diagnosis was nasopharyngitis. The most frequent respiratory symptoms were nasal discharge (82.1%) and cough (80.4%). Around 6.1% of the total number of the cases were due to pneumonia (77.7% of the cases involving hospitalization). There were no associations of ARI with children's nutritional status, family income or passive smoking. There was statistical association between maternal educational status and ALRI (c 2 = 16.57).Conclusions: The findings show that most of the children presented nasopharyngitis (UAI), being most of them male. Pneumonia (ALRI) was the main cause of hospitalization. The most common symptoms were nasal discharge and cough. Besides, the most important risk factor associated was the mother's educational status. J. pediatr. (Rio J. IntroduçãoAs infecções respiratórias agudas (IRA) são mundialmente reconhecidas como sendo uma das principais causas de morbidade e mortalidade em todas as idades, particularmente em crianças 1,2 . Nos países desenvolvidos assim como nos em desenvolvimento, a morbidade da IRA é semelhante, entretanto nos países em desenvolvimento a mortalidade é superior, alcançando até trinta vezes ou mais 1,3,4 . A alta taxa de morbidade faz da IRA a principal causa de utilização dos serviços de saúde, representando em todo o mundo de 20 a 40% das consultas em serviços de pediatria e 12 a 35% das internações hospitalares 3 . As pneumonias, de acordo com dados da OPAS/OMS 5 , são as responsáveis por 20 a 40% das hospitalizações de menores de cinco anos nos países em desenvolvimento. Em zona