Background: Thoracoabdominal mobility (TAM) in newborns (NB) is an important respiratory function parameter in clinical assessment. Different systems have been proposed to assess compartmental mobility in a number of pathologies and age ranges. The present study aimed to verify the inter and intraexaminer reliability of an interactive custom-made MATLAB® App for bio-photogrammetric analysis of thoracoabdominal mobility in newborns (NB) and compare the respiratory rate (RR) results between the automatic MATLAB® App and its manual counterpart.Methods: This is a cross-sectional study conducted in 27 healthy NB of both sexes (gestational age between 37 and 41 weeks and up to 72 hours of life) who did not cry during data acquisition. Chest and abdominal areas of the NB in the supine position were analyzed through 60s videos, totaling 30,714 photograms. All photograms were analyzed by three examiners on three different occasions. Analysis of variance (ANOVA) and intraclass correlation coe cient (ICC) were applied, adopting a 95% con dence interval and signi cance level of α = 0.05.Results: Reliability was excellent for intra (ICC 0.81 -0.96) and inter-examiner correlations (ICC 0.84-0.99) between the chest and abdominal areas, in both inspiration and expiration, with no differences between them.Conclusions: Evaluation of NB thoracoabdominal mobility using the custom-made MATLAB® App for bio-photogrammetric analysis exhibited good to excellent intra-and inter-examiner reliability and an