Aim: In this review, we aim to describe how exhaled Nitric Oxide(NO) changes during the first months of life in premature and mature infants. Method: Review of the literature up to August 2020, on online, tidal breathing NO measurements in unsedated infants. The association between Fractional exhaled NO(FeNO) values, postnatal age, and prematurity was analysed using linear mixed modeling and Spearman's rank correlation. Results: Median FeNO during the first months of life was 5.9 and 8.5 ppb in premature and mature infants, respectively. The linear mixed model analysis showed a significant effect of postnatal age on FeNO (p = 0.007). Conclusion: Our study suggests that FeNO is higher in mature infants than premature infants, and FeNO increased with postnatal age at approximately the same pace in both groups.