Poor maternal diet in pregnancy can influence fetal growth and development. We tested the hypothesis that poor maternal diet quality during pregnancy would increase neonatal adiposity (percent fat mass (%FM)) at birth by increasing the fat mass (FM) component of neonatal body composition. Our analysis was conducted using a prebirth observational cohort of 1079 mother-offspring pairs. Pregnancy diet was assessed via repeated Automated Self-Administered 24-h dietary recalls, from which Healthy Eating Index-2010 (HEI-2010) scores were calculated for each mother. HEI-2010 was dichotomized into scores of ⩽57 and >57, with low scores representing poorer diet quality. Neonatal %FM was assessed within 72 h after birth with air displacement plethysmography. Using univariate and multivariate linear models, we analyzed the relationship between maternal diet quality and neonatal %FM, FM, and fat-free mass (FFM) while adjusting for prepregnancy body mass index (BMI), physical activity, maternal age, smoking, energy intake, preeclampsia, hypertension, infant sex and gestational age. Total HEI-2010 score ranged between 18.2 and 89.5 (mean: 54.2, s.d.: 13.6). An HEI-2010 score of ⩽57 was significantly associated with higher neonatal %FM (β=0.58, 95% confidence interval (CI) 0.07-1.1, P<0.05) and FM (β=20.74; 95% CI 1.49-40.0; P<0.05) but no difference in FFM. Poor diet quality during pregnancy increases neonatal adiposity independent of maternal prepregnancy BMI and total caloric intake. This further implicates maternal diet as a potentially important exposure for fetal adiposity.