[영문]The impact of healthcare interventions on health utility values is most frequently measured using a preferencebased instrument. Each of the available instruments instructs the respondent to report their health status over different recall periods ranging from the current day to the past month. In an ongoing randomised controlled trial in patients with advanced HIV disease, the impact of using a preferencebased instrument with a 1week recall period vs a 1day recall period e.g. today for capturing recently resolved serious adverse events was measured. The results suggest that the instrument with a 1week recall period gave lower utility values for recently resolved events in comparison with the instrument with a 1day recall period. A plausible interpretation of these results is that the recall period was adhered to; for example, patients ignored the impact of recently resolved events in their response if the questionnaire asked them only about their health today. While there are limitations to our study, we believe further consideration should be given to the recall period used for preferencebased instruments, and future research should examine other patient groups using a single instrument with multiple recall periods