In contrast to the well-observed associations between obesity, diabetes, and autism spectrum disorder (ASD), the roles of maternal dyslipidemia and sex disparity in ASD have not been well-studied. We examined the joint associations of maternal plasma cholesterols, branched-chain amino acids (BCAAs) and child sex on child ASD risk. We analyzed data from 756 mother-infant pairs (86 ASD) from the Boston Birth Cohort. Maternal plasma cholesterols and BCAAs were measured in samples collected 24-72 h postpartum. We found that in this urban, low-income prospective birth cohort, low maternal high-density lipoprotein cholesterol (HDL-C), above-median maternal plasma BCAA concentrations, and male sex additively or synergistically increased risk of ASD. Additional studies are necessary to confirm our findings.