SUMMARY The dynamics of influenza A viral load in respiratory samples collected from adult A(H1N1)pdm09 influenza patients were investigated. Three respiratory specimens were obtained every 2-4 days and clinical findings were recorded at the time each specimen was collected. A total of 105 serial specimens were collected from 35 patients. Viral clearance was more rapid in patients aged 15-29 years than patients aged 30-49 years (P < 0·01) or ?50 years (P < 0·01). Hospitalized patients showed slow viral clearance compared to outpatients (P < 0·01). Resolution of cough and headache was correlated with viral load reduction in respiratory specimens. Viral shedding was found in 17 patients (48·6%) 5 days after symptom onset. Time to hospital visit after symptom onset was significantly correlated with prolonged viral shedding (odds ratio 9·0, 95% confidence interval 1·56-51·87, P = 0·01). These findings will contribute to infection control aspects with respect to managing patients with influenza virus infections.