Approximately 30 influenza A(H3N2) isolates for each year of 1997-2006 obtained from the nasopharyngeal aspirates (NPAs) of children aged 1-10 years, admitted to the Prince of Wales Hospital (PWH) in Hong Kong, were retrieved from long-term archives (stored either at 270uC or in liquid nitrogen) for hemagglutinin (HA) and neuraminidase (NA) gene sequencing and analysis. These children presented with acute respiratory illness and did not receive anti-influenza therapy before or during their illness. As influenza A(H1N1) was the predominant circulating virus during 2006, very few H3N2 isolates were obtained for that year. Table 1 shows the age and sex distribution of these children.