OBJECTIVE: The purpose of this study was to estimate biases in recalling alcohol consumption over short periods. METHOD: Patients (n = 918) attending the surgical ward of the emergency department (ED) of the Lausanne University Hospital in Switzerland participated in a brief intervention study. Inclusion criteria were an average alcohol consumption exceeding 14 drinks per week for men or 7 drinks per week for women, or the consumption at least once monthly of 5 or more drinks for men or 4 or more drinks for women. Alcohol consumption was measured by means of a retrospective 7-day diary. RESULTS: Recalled alcohol consumption decreased with the length of the recall period. Consumption was 0.9 drinks lower for a recall of 7 days compared with a recall of 1 day. Biases were apparent for every day of the week, but the bias was highest for consumption to be recalled for Fridays and Saturdays. Recall bias was significant only for sporadic drinkers (those drinking less than 4 days a week) but not for regular drinkers (those drinking 5 or more days a week). CONCLUSIONS: Recall bias is a threat for survey measurements of alcohol consumption in general and particularly for research designs in which the bias is differentially distributed across cases and controls. This bias is true for case-crossover designs in which the recalled consumption of an individual for a period farther away from the interview (e.g., past week) serves as the control for the acute intake of the same individual (e.g., in the 6-hour period preceding ED attendance). Because risk estimates of case-crossover designs focus particularly on sporadic drinkers, the finding of recall biases being higher among sporadic drinkers increases the chance of spurious findings in such designs.