Sixty-four adults participated in a study examining the accuracy of metacognitive judgments during 28 hr of sleep deprivation (SD) and continuous cognitive work. Three tasks were studied (perceptual comparison, general knowledge, and mental addition), collectively spanning a range of cognitive abilities and levels of susceptibility to SD. Subjective and objective measures of sleepiness confirmed the expected patterns of increasing fatigue with SD. Participants displayed differing levels of metacognitive abilities across tasks, but traditional indices of the confidence-accuracy relation (i.e., calibration, resolution, over- and underconfidence), as well as the accuracy of pre- and posttask estimates of performance, remained stable over the SD period. The findings suggest that people can accurately assess their own cognitive performance when deprived of 1 night of sleep and that this ability need not be based on subjective estimates of sleepiness. The implications and limitations of the study are discussed and directions for future research are proposed.