The measurement of dietary intake by self-report has played a central role in nutritional science for decades. Despite its important role, however, little is known about the accuracy of self-reported intake. Recently, the doubly-labeled water method has been validated for the measurement of total energy expenditure in free-living subjects, and this method can serve as a reference for validating the accuracy of self-reported energy intake. Such comparisons have been made in nine recent studies, and considerable inaccuracy in self-reports of energy intake has been documented. Reported intakes tend to be lower than expenditure and thus are often underestimates of true habitual energy intake. Because the degree of underreporting increases with intake, it is speculated that individuals tend to report intakes that are closer to perceived norms than to actual intake.