PURPOSE: this study seeks to analyse the results of neonatal auditory screening by means of transient otoacoustic emissions in newborn babies in relation to their different lifespans. METHOD: the medical charts of 1689 babies, previously analysed in 2008, were evaluated in two maternity wards of SC. The babies were divided into two groups: in group 1 screening had been completed in the first 24 hours after birth, and in group 2, it had been completed between 24 and 48 hours after the babies' birth. RESULTS: in group 1, of the 894 babies submitted to NAC, the index of "failure" was 4.5%, equivalent to 39 babies. In group 2, of the 795 babies and 1.5% (12) "failed" the test. The findings demonstrated that NAC carried out by means of TOAE in the babies during the first 24 hours of birth presented a higher "failure" index than NAC completed after 48 hours of birth. CONCLUSION: NAC should be completed at the maternity wards before hospital discharge, but only after the first 24 hours of life due to the great incidence of artifacts that may be encountered.