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Background To better characterise prematurity-associated lung disease, adult spirometry phenotype classifications (obstructive lung disease, preserved ratio impaired spirometry and dysanapsis) have been applied to children born preterm. It is unknown how these phenotypes track over time.Aim Apply spirometry phenotype classifications to a longitudinal cohort born very preterm (≤32 weeks gestation) and track changes in classifications from early childhood to adolescence.Methods This retrospective longitudinal cohort study included children born very preterm in Western Australia between 1997 and 2003, followed up between 2007 and 2022. Spirometry testing and a modified International Study of Asthma and Allergies in Childhood questionnaire were completed at early childhood (4–8 years), middle childhood (9–12 years) and adolescence (16–23 years). Spirometry phenotype classifications were applied to each participant with acceptable spirometry at each time point.Results 200 participants completed 311 acceptable spirometry measurements. Abnormal spirometry phenotypes were observed in 29% of participants at early childhood, 41% at middle childhood and 43% at adolescence. Of those with spirometry measurements across at least two time points, 36% changed phenotypes (e.g. from normal to abnormal, from abnormal to normal or changed between the abnormal groups). Many of those that changed phenotype classification had a forced expiratory volume in 1 s (FEV 1) z-score or FEV1 to forced vital capacity (FVC) ratio z-score sitting near the lower limits.Conclusion It remains unclear whether changes in phenotype reflects the biological variability of the measure or disease progression. The instability of adult spirometry classifications across serial spirometry measurements suggests this approach does not adequately capture the complexity of prematurity-associated lung disease during the growth period.