BACKGROUND: There is little epidemiologic evidence to assess the maturation of respiratory control in premature infants. OBJECTIVE: To measure the success rate or the percentage of infants who have no additional events of various apnea- or bradycardia-free intervals after correcting for gestational age, postmenstrual age of the last apnea or bradycardia event, and the severity of the event. METHODS: This was a retrospective cohort study of infants born at 34 weeks’ gestational age or earlier at 1 of 5 Kaiser Permanente Medical Care Program hospitals between 1998 and 2001. The success rates of various apnea- or bradycardia-free intervals were calculated after stratifying according to gestational age, postmenstrual age of the last event, or event severity. RESULTS: Among the 1403 infants identified in this study, 84.2% did not have an apnea event and 78.5% did not have a bradycardia event after they were otherwise ready for discharge. For the entire cohort, a 95% success rate was statistically reached, with a 7-day apnea- or bradycardia-free interval. Infants with a gestational age of 30 weeks or less had a 5% to 15% lower success rate than infants with a gestational age more than 30 weeks for any given apnea- or bradycardia-free interval. The success rate was reduced by an additional 5% to 10% if the last apnea or bradycardia event occurred at a postmenstrual age of more than 36 weeks. Including only the most severe events slightly improved the success rate of a given interval. CONCLUSIONS: The risk of recurrence for apnea or bradycardia differs depending on the gestational age of the infant and the postmenstrual age of the last apnea or bradycardia event.