***Motor development in the first year of life of premature infants according to birth weight***AIMS: To assess motor development in the first year of life of children born at 36 weeks' gestational age, comparing two groups, one with birth weight below 2500g and the other with 2500g or more.METHODS: A cross-sectional study evaluated the motor development of children enrolled in the Basic Health Units of Caxias do Sul and Porto Alegre, by the Alberta Infant Motor Scale. The sample consisted of infants born at 36 weeks' gestation, evaluated with a corrected chronological age of 0 to 12 months, divided into two groups: Low Birth Weight group (LBW group: birth weight below 2,500 g) and Adequate Birth Weight group (ABW group: birth weight of 2,500 g or more). The independent t-test, the chi-square test of Pearson and the Eta2 test (strong association> 0.60) were used to analyze the data. P <0.05 was considered significant.RESULTS: We evaluated 42 children, 21 in each group. Fifteen (71.42%) children with low birth weight were classified as small for gestational age. The mean motor development score percentile was 17.90±17.74 for the LBW group and 34.57±25.80 for the ABW group, indicating a better motor development of the second group (p=0.02) . There was a greater number of children with developmental delay in the LBW group (52.4%), whereas in the ABW group most were within the normal range (47.6%). The association was statistically significant between performance categories and birth weight groups, using the chi-square test (p=0.001), with Eta2=0.64 (strong association).CONCLUSIONS: In preterm infants with matched gestational age at 36 weeks, the low birth weight group had worse motor performance in the first year of life compared to the group with adequate birth weight.