Respiratory tract infections (RTIs) constitute the major cause of illness and mortalities in infants and children worldwide. Viruses account for 50-90% of the reported cases, with over 80% attributed to six viruses: respiratory syncytial virus (RSV), parainfluenza viruses (types 1-3) and influenza viruses (types A and B). In Saudi Arabia, there is a substantial lack of information regarding the prevalent respiratory viruses in terms of predominant types and subtypes, risk factors and virus diversity/phylogeny. To highlight the epidemiology and characteristics of respiratory viruses circulating among Saudi population, 260 nasopharyngeal aspirates (NPAs) were obtained from young children hospitalized with acute RTIs at 3 hospitals in Riyadh during the winters of 2007/08, 2008/09 and 2010/11. All samples were screened for the six principal respiratory viruses using monoplex and multiplex RT-PCR assays. The results identified 42 (16.2%) RSV (26 type A and 16 type B), 36 (13.85%) influenza A, 4 (1.54%) influenza B, 10 (3.85%) parainfluenza 3 virus, and 1 (0.38%) parainfluenza 2 virus positive samples. Propagation of positive samples in cell culture (Vero and HEp2) and embryonating eggs led to the recovery of two RSV type A, two influenza B virus, and one parainfluenza 3 virus isolates. Characterization of these isolates using ELISA, immunofluorescence, and virus neutralization further established their identity. Molecular characteristics of Saudi strains were partially elucidated by analysis of the entire sequence of the major viral protein genes (haemagglutinin and neuraminidase of influenza viruses, attachment and fusion of RSV, and haemagglutinin-neuramindase of parainfluenza viruses). The genetic diversity and phylogenetic relationship of Saudi strains with the different strains circulating globally were studied to understand their circulation pattern and genetic evolution.