OBJECTIVE: To investigate the intention of the Hong Kong general population to take up vaccination against influenza A/H1N1. Setting Cross sectional population based anonymous survey. Participants Random sample of 301 adults interviewed by telephone (response rate 80%). MAIN OUTCOME MEASURE: Intention to take up vaccination against influenza A/H1N1 under five hypothetical scenarios: vaccination is free; vaccination per dosage costs less than $HK100 ( pound8; euro9; $13), $HK101-200, or more than $HK200; and no data are available on the efficacy and safety of the vaccine. Results 45% (n=135) of the participants reported that they would be highly likely take up vaccination if it was free. When vaccination incurred a cost, however, the prevalence of uptake decreased: 36% (n=108) would take up vaccination if it cost less than $HK100, 24% (n=72) if it cost $HK101-200, and 15% (n=45) if it cost more than $HK200; and in absence of proved efficacy and safety decreased to 5% (n=14). Moreover, 32% (n=95) considered universal A/H1N1 vaccination unnecessary. Overall, 39% (n=117) of participants believed that A/H1N1 vaccination would prevent the virus being contracted; 63% (n=189) erroneously believed that efficacy of the vaccine had been confirmed by clinical trials, and 16% (n=49) believed that it is necessary for everyone in Hong Kong to take up vaccination against influenza A/H1N1. Conclusions The uptake of vaccination against influenza A/H1N1 by the general population of Hong Kong is unlikely to be high and would be sensitive to personal cost. Evidence about safety and efficacy is critical in determining the prevalence of uptake of vaccination.