This was a cross sectional study to determine the clinical, laboratory and radiologic characteristics of confirmed avian influenza (AI) (H5N1) infection among children and adults. This study was conducted at Sulianti Saroso Infectious Diseases Hospital (SS-IDH), Jakarta among subjects confirmed to have AI infection hospitalized during September 2005 to August 2010. The proportion of confirmed AI patients was 33 out of 321 suspected and probable cases (10.2%). Of 26 subjects analyzed (7 subjects was excluded due to loss of or incomplete medical records), the median ages were 7 years and 25 years in children and adults, respectively (range 1 - 39 years). Prominent clinical features were respiratory symptoms [productive cough (13/13 children; 12/13 adults), dyspnea (12/13 children; 13/13 adults)], and fever (12/13 children; 12/13 adults). Leukopenia was found in 9 subjects in each group. Four children and 7 adults had lymphopenia, while thrombocytopenia was found in 7 children and 10 adults. Two children had an increased ALT, while most adults had an increased AST (10/13) and/or ALT (8/13). Bilateral infiltrates found in most subjects on chest x-ray who had clinical deterioration. Of the 3 children who survived out of 13 children with AI, they all had less severe clinical features and no central nervous system involvement, lymphopenia, thrombocytopenia, or increased creatinine level. None of the adults survived.