To determine viral causes of acute upper respiratory tract infections and clinical findings in children living in Istanbul, Turkey. This prospective study was carried out in 234 outpatient children (age range: 1-180 months) with acute upper respiratory tract infections, seen in the outpatient clinic at Istanbul Medical School Childrens Hospital. After clinical findings were recorded, nasal swab specimens were taken. In 201 specimens collected, influenza-A and-B, adenovirus, respiratory syncytial virus, and parainfluenza viruses were studied using direct fluorescence antibody, polymerase chain reaction (PCR), and cell culture techniques. Rate of virus isolation was 29.8%(60/201). The viruses isolated in decreasing order were influenza-A (36.6%), adenovirus (28.4%), parainfluenza (14.9%), and respiratory syncytial virus (13.5%). All influenza-A cases were type H3N2. The common viruses in children less than 2 years of age were respiratory syncytial virus (63%) and adenovirus (59%), whereas influenza-A was dominant over 2 years of age (82%). Clinical symptoms did not differ among the different viral causes. Viral etiologies in children with acute upper respiratory tract infections were shown at a rate of 29.8% and the most common causes were influenza-A, adenovirus and parainfluenza viruses.