BACKGROUND : We have previously reported that in utero arsenic exposure is associated with increased length and other anthropometric outcomes at birth in a U.S. cohort. However, it is unknown whether these anthropometric differences persist through early life. OBJECTIVE : We assessed in utero arsenic exposure in relation to attained anthropometry and growth trajectories through the first year of life. METHODS : Among 760 mother-infant pairs from the New Hampshire Birth Cohort Study, we assessed in utero arsenic exposure using maternal second trimester urinary arsenic and assessed infant growth from medical records. RESULTS : Median maternal second trimester total urinary arsenic (tAs; inorganic arsenic + monomethylarsonic acid + dimethylarsinic acid) was 3.96 μg/L (IQR: 2.02, 6.72). In adjusted linear mixed effects models, each doubling of maternal urinary tAs was associated with a 0.05 increase in length WHO Z score (95% CI: 0, 0.09) over the first year of life which corresponds to an approximately 0.12 cm increase in males and 0.13 cm increase in females at 12 months. No associations were observed between urinary tAs and attained weight, weight-for-length, or head circumference. In adjusted piecewise linear mixed effects models, each doubling of urinary tAs was associated with a 0.07 (95% CI: 0.02, 0.12) cm per month decreased length growth rate through 3.5 months with no evidence of an association thereafter. No associations were observed between urinary tAs and infant weight gain or change in weight-for-length and head circumference through one year. CONCLUSIONS : On average, infants exposed to higher in utero arsenic attained modestly longer length during the first year, despite having slower linear growth in the first 3.5 months of life. This suggests that the previously demonstrated arsenic-associated longer length among study infants at birth persists through the first year of life. No other anthropometric associations with in utero arsenic exposure were observed across the full study population.