BACKGROUND: Preterm birth induces structural and functional remodeling of multiple organ systems during a critical period of development. Imbalance in body composition can be one of these outcomes and studies with premature babies (PTNB) reported that body composition seems to interfere with lung function and motor performance, however the association between muscle mass and motor performance in this population is unclear.OBJECTIVE: Correlate skeletal muscle size and quality with motor performance in the PTNB, comparing their term peers (TNB). METHODS: Cross-sectional study in which birth data and anthropometric characteristics were collected. Ultrasonography was performed to evaluate the cross-sectional area and pennation angle of the rectus femoris, tibialis anterior and biceps brachii muscles, and an evaluation was performed using the Test Infant Motor Performance (TIMP). RESULTS:53 newborns (NB) who met the inclusion criteria were evaluated. They were divided into 2 groups PTNB (n=27) and TNB (n=26). The groups showed differences in anthropometric and in the cross-sectional area of the biceps (55.52 ±9 cm2 TNB x 49.6 ± 7.3 cm2 PTNB p=0.01); thigh circumference (16.1±3 cm TNB x 13.2±3.2 cm PTNB p<0.002); TIMP score (79.4±23 TNB x 48.2±19 PTNB p<0.0001); Several variables showed a moderate positive correlation showing an association between area, muscle belly size and pennation angle with the TIMP score. CONCLUSION: there is a moderate association between size and peripheral muscle strength with measures of motor performance in NB. The PTNB have lower values in the evaluated variables when compared to the TNB. These variables can already be assessed early.