Premature birth brings numerous systemic repercussions for the newborn (NB), it is observed that this global immaturity affects the performance of the respiratory muscles and not only the lungs. There is also a parallelism between motor development and respiratory muscle performance, however this relationship is not directly described in the literature. AIM: To evaluate the relationship between the strength and function of the respiratory muscles and the motor performance of premature newborns (PTNB) and their term peers (TNB). Methods: Cross-sectional study in which birth data and anthropometric characteristics were collected. Ultrasonography was performed to evaluate the diaphragm (thickening fraction and  excursion), parasternal muscles (activation and thickening) and a motor assessment using the Test Infant Motor Performance (TIMP). Results: 53 newborns (NB) were evaluated. They were divided into 2 groups PTNB (n=27) and TNB (n=26). The groups showed differences in anthropometric and assessment variables at birth. The PTNB showed lower DTF% values 54.8±48 x 36.7±25.6 p=0.04 ; there was a moderate negative correlation between thickening of the parasternal muscles and the TIMP score (R= -0.43 p=0.02), the PTNB group had a higher parasternal activation. Conclusion: PTNB have a lower degree of diaphragmatic thickening, which is strongly related to muscle strength and greater activation of parasternal  and this is negatively related to motor performance, suggesting that babies with greater activation of rib cage muscles and lower diaphragm strenght may have lower motor performance.