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Background: Correlated long-range fluctuations of lung function have been demonstrated in asthmatic adults. Objective: To determine the pattern of FEV1 fluctuation and its potential age dependence in healthy children and adolescents. Methods: The study of lung function variability in children and adolescents (NCT04163146) includes subjects aged 6-18 years who perform spirometry twice daily for 3 months (180 trials) using a portable device (Spirobank Smart). Here, we applied detrended fluctuation and sample entropy (SampEn) analysis to FEV1 data of healthy participants (no asthma, normal baseline spirometry). We evaluated the scaling exponent α (long-range correlations) and SampEn (regularity of data series) of consecutive FEV1 recordings in relation to age. Results: Our preliminary results (N=11; target >75) indicate the presence of correlated long-range (over weeks/months) fluctuations of FEV1. The scaling exponent α decreases with increasing age (r –0.738; P=0.0095) while SampEn increases (r 0.694; P=0.0178) (Figure). Conclusions: Healthy children and adolescents present correlated long-range fluctuations of FEV1, the pattern of which changes with age. Our findings suggest that developmental aspects may influence the complex temporal interaction between environmental stimuli and airway tone, hypothetically affecting the stability and adaptability of the respiratory system.