An adverse fetal environment leads to smaller kidneys, with fewer nephrons, which might predispose an individual to the development of kidney disease and hypertension in adult life. In a prospective cohort study among 1,072 children followed from early fetal life onward, we examined whether maternal smoking during pregnancy, as a significant adverse fetal exposure, is associated with fetal (third trimester of pregnancy, n = 1,031) and infant kidney volume (2 years of age, n = 538) measured by ultrasound. Analyses were adjusted for various potential confounders. Among mothers who continued smoking, we observed dose-dependent associations between the number of cigarettes smoked during pregnancy and kidney volume in fetal life. Smoking less than five cigarettes per day was associated with larger fetal combined kidney volume, while smoking more than ten cigarettes per day tended to be associated with smaller fetal combined kidney volume (p for trend: 0.002). This pattern was not significant for kidney volume at the age of 2 years. Our results suggest that smoking during pregnancy might affect kidney development in fetal life with a dose-dependent relationship. Further studies are needed to assess the underlying mechanisms and whether these differences in fetal kidney volume have postnatal consequences for kidney function and blood pressure.