There are limited data on the risks of aneuploidy for normal-appearing fetuses with amniotic fluid volume (AFV) abnormalities. The purpose of this study was to determine the relative risks of aneuploidy associated with second-trimester abnormal AFVs and fetal structural anomalies in a cohort of 2,823 singleton, viable fetuses. Compared to gravidas younger than 35 with normal ultrasounds, normal fetuses had an increased incidence of aneuploidy with polyhydramnios, increased AFV, i.e. subjectively increased but normal by maximum vertical pocket (MVP) and/or amniotic fluid index (AFI), oligohydramnios, and decreased AFV, i.e. subjectively decreased but normal by MVP and/or AFI. These included: increased AFV [odds ratio = 12.9, 95% confidence interval (CI) = 4.1-39.4], polyhydramnios (odds ratio = 4.6, CI = 0.6-36.8), and decreased AFV (odds ratio = 3.8, CI = 1.1-13.1). There were no aneuploidies among the 28 normal fetuses with oligohydramnios. Anomalous fetuses had a markedly increased incidence of aneuploidy (odds ratio = 13.4, CI = 7.2-24.9). We conclude that fetal structural anomalies as well as isolated AFV abnormalities were associated with an increased risk for aneuploidy.