The development of pathologic apnea, respiratory pauses, and periodic respiration was examined in 71 high-risk preterm infants, observed weekly. Respiration was recorded every 10 seconds; apnea length and periodic inspiration were scored from a tape. All subjects had respiratory pauses, and 36 had pathologic apnea. The mean length of respiratory pauses was longer in quiet sleep, and the frequency of respiratory pauses was greater in active sleep. The mean length of respiratory pauses and probability of pathologic apnea in both sleep states and frequency of pauses in quiet sleep decreased with age. Sex, theophylline treatment, race, and length of mechanical ventilation affected the developmental trajectories of some apnea variables. Apnea in preterm, infants cannot be considered a unitary phenomenon. © Lippincott-Raven Publishers.