A longitudinal study of normal fetal growth is presented as a basis for prenatal diagnosis of skeletal dysplasias. The lengths of fetal limb bones, abdominal circumference, thoracic circumference, head circumference, foot length and orbital diameters were measured in 63 normal fetuses between 12 and 40 weeks of gestation. From these data, ratios were calculated which may have relevance for the prenatal diagnosis of skeletal dysplasias. In addition, rates were calculated for fetal limb growth. From these parameters (absolute measurements, ratios and growth rates), the 10th, 50th and 90th centiles were determined as reference values.