SUMMARY The antagonistic effects of extensive sleep deprivation (SD) on human cognitive performance are well documented. However, one aspect of human performance that has not been investigated with respect to its susceptibility to SD is the ‘metacognitive’ ability to self‐monitor overt performance. In the present study, 16 male subjects participated in an experiment requiring sustained cognitive work during a three day period. One of the cognitive tasks required the mental addition of rapidly presented numbers. On each trial, subjects reported the sum and then provided a subjective confidence rating to indicate the degree of certainty in their response. As expected, performance on the sequential addition task deteriorated with increasing fatigue and returned to baseline following a recovery sleep. However,calibrationanalyses, which quantify a number of properties of the relationship between subjective and overt performance, revealed that the correlation between confidence and performance (calibration), the ability to differentiate correct from incorrect judgments (resolution), and validity of subjective ‘certainty’, were all unaffected by SD. Hence, in the absence of external feedback from the environment, people have access to fairly reliable internal feedback about their performance during periods of sustained and vigilant cogniti