The sleep patterns of 41 full-term newborn infants were recorded continuously during the first 2 postnatal days. The recordings were made nonintrusively using the Motility Monitoring System while the infants were in the hospital. When the subjects were 8 months old, their mothers filled out the Infant Temperament Questionnaire, which yields scores on nine dimensions of temperament. There were four significant correlations between Day 1 sleep measures and later temperament dimensions; there were eight correlations on Day 2, hardly more than a chance number. The temperament scores were used to classify infants as having Easy, Intermediate, Difficult, or Most Difficult temperament. Profiles of sleep measures for the infants in the four groups differed significantly on Day 1, and the Most Difficult infants showed the most extreme values on all measures. Differences in the predictive findings from Day 1 and Day 2 were attributed to the greater influence of the stress of labor and delivery on the first postnatal day.