The authors report a prospective study conducted in one of the general pediatrics unit. One hundred one children, aged 20 days to 12 years, admitted with acute lower respiratory tract infections have been studied on clinical paraclinicals and etiology grounds. All children had a chest Ray roentgenogram, a total blood cell count and C-reactive protein. The detection of a viral agent in nasopharyngeal aspirate by immunofluorescent technic were performed. 85% of patients have bronchiolitis, the chest--Rays showed an abnormal pictures in 84.2% of cases, an anaemia was present in 54.7%. Viral agent as identified in 58 patients, the RSV indicated in 56 cases. Bacterial infection as present in 57 of the 101 children. A mixed viral-bacterial infection as documented in 28 cases. Among bacterial causes the predominant agent as Haemophilus influenzae 24, Branhamella Catarrhalis 17, streptococcus pneumoniae in 16 cases. Early empiric antibiotic as performed. All patients recovered uneventfully.