The incidence of apnea and periodic breathing was studied in full-term infants between birth and 6 months of age. Apnea was defined as a pause equal to or exceeding six seconds, periodic breathing as two cessations of breathing within a 20-second period, each equal to or longer than three seconds but less than six seconds. Sleep and cardiopulmonary variables were monitored. Apnea was common in the normal full-term infant. The incidence of apnea was highest in the newborn period and apneas exceeding 15 seconds were limited to this age. A reduction in apnea incidence occurred between birth and 3 months of age; thereafter, the incidence remained unchanged. The majority of apneas occurred during active sleep (AS). Few minutes were classified as indeterminate; the number of apneas during these minutes was comparable to those during AS. The incidence of apneas during quiet sleep was low. Periodic breathing remained stable across the ages, occurring primarily in AS. Apnea exceeding 15 seconds in rare in infancy. The tabulation of shorter apnea may be of limited value in identifying infants at risk for abnormal apnea due to extreme variability among infants. The sleep-waking state of the infants must be considered in order to evaluate apnea counts.