We developed a nomogram for transverse cerebellar diameter (TCD) in Thai fetuses by recruitment of 153 normal pregnant women in the first trimester. The gestational age calculated by the certain last menstrual period and the first trimester ultrasound were in agreement. The pregnant women were stratified into 4 groups and scanned at four weekly intervals: group A was first scanned at 14 weeks, group B at 15 weeks, group C at 16 weeks, and group D at 17 weeks. A total of 699 measurements from 14 to 40 weeks of gestation were obtained. The data were analyzed for mean and standard deviation; and the best fit mathematical model was derived. The TCD grew progressively along gestational age. The growth rate was slightly less than that of a Western study after 28 weeks of gestation. This could serve as the basis for gestational dating in fetuses with aberrant fetal growth.