Summary: Two groups of infants (40 normal full-term, 24 prematurely born infants) were matched on conceptional age and were studied at seven ages during the first year of life, All-night time-lapse video somnography was obtained in the home at 2, 4, 8, 20, 24, 36, and 52 weeks of age. The developmental course of sleep-wake state proportions, sleep onset indices, and special variables assessing temporal organization are compared. Age-appropriate developmental norms for sleep-wake state assessment during the first year of life are presented, using video somnography. In general, sleep-wake state ontogenesis is comparable in the two groups. The premature group is more variable from one age to the next, even though both groups demonstrate significant individual stability of some sleepwake variables over the first year of life. Key Words: Sleep-wake state-Gestational age-Active sleep-Quiet sleep.Sleep difficulties in infants from birth to 3 years have become one of the most common problems of pediatric practice. Usually the disturbances are short -lived and probably without long-term consequences, although sleep habits of young infants may reflect longer lasting temperamental characteristics or aspects of dyadic interaction that herald later childhood and adult sleep patterns. Given the prevalence of the problem in the pediatric age group, it is surprising how little longitudinal data exist describing the ontogenesis of sleep-wake patterns in normal infants.Cross-sectional studies during infancy and childhood have repeatedly confirmed that developmental changes of REM sleep, NREM sleep, and waking do occur (1)(2)(3)(4)(5)(6)(7)(8)(9). The studies confirm that, by and large, the REM state predominates in immature infants and declines during maturation, sleep onsets from wakefulness are to the REM state during the early months of life and to the NREM state later, diurnal influences on REM/NREM organization during the night emerge gradually, and poor epoch-by-epoch coordination of physiological systems results in immature sleep state organization (indeterminate states) in