Study on clinical features and epidemiology among 10 patients had avian influenza A who treated in hospital in Ho Chi Minh City and Ha Noi 12/2003 and 1/2004, 13,7 mean age. In all patients, the diagnosis of influenza A (H5N1) was confirmed by means of viral culture or reverse transcriptase polymerase chain reaction (RT-PCR) with primers specific for H5 and N1. None of the 10 patients had pre-existing medical conditions. Nine patients had a clear history of direct contact with poultry. All patients had fever, respiratory symptoms and clinically significant lymphopenia. The medium platelet count was 75.500/mm3. Seven patients had diarrhea. In all patients, there were marked abnormalities on chest radiography. There was no definitive evidence of human to human transmission, eight patients died