To determine the effect of implementing the American Academy of Pediatrics (AAP) recommendation that premature infants of less than 37 weeks' gestation have a period of monitoring in their car seat before discharge, a prospective, hospital-based population study in which infants were evaluated for the presence of apnea, bradycardia, and/or hypoxemia in their crib and car seats before discharge was performed. All infants of less than 37 weeks' gestational age were assessed before discharge. One hundred and forty-one infants were studied, 123 of whom had a complete assessment for the presence or absence of significant apnea and/or hypoxemia in their crib and car seat. Twenty-nine of 123 infants (24%) met predetermined criteria for failure. Infants who failed had a greater frequency of diagnosis of apnea of prematurity (P=0.023) and were more frequently male (P=0.048). All of the 29 who met failure criteria experienced significant desaturation while in their car seat. Apnea occurred in 12 of these infants. Desaturation during periodicity occurred in seven infants. Of the failure group, 18 had the desaturation corrected following repositioning. Of the remaining 11 failures, four required oxygen in their car seat: one required vigorous stimulation; one was restarted on theophylline; and two were restarted on a cardiac monitor. All 11 infants had their discharge delayed from one to 20 days and were restudied one to three times, with one infant returning after discharge for an out-patient reassessment at 40 weeks' adjusted age. In conclusion, a car seat assessment should be part of the prehospital discharge planning for premature infants, in keeping with the AAP's recommendations.