Subtle facial abnormalities, including smallness of the nose, are common findings in trisomy 21 and numerous other genetic conditions. The aim of this study was to construct a normal range for the length of the fetal nasal bones with gestation in a Caucasian population. Ultrasound measurements were performed on a strictly mid-sagittal profile in 376 normal singleton fetuses at 14-34 (mean 24) weeks' gestation. It was found that the length of the nasal bones increased from 4 mm at 14 weeks to 12 mm at 35 weeks' gestation, and that there was a linear relationship between the length of these bones and biparietal diameter and femur length. We conclude that the length of nasal bones can easily be measured in fetuses at 14-34 weeks' gestation and that such measurements might prove useful in the evaluation of pregnancies at high risk for associated fetal abnormalities.