We have followed fetal growth by ultrasonographic B-scans. In addition to percentile curves of the biparietal skull diameter we have established percentile curves for measurements of the fetal trunk (sagittal thoracic diameter and length of trunk). The percentile curves for the biparietal diameter were obtained from 5400 individual measurements; the percentile curves for the trunk measurements utilized 1300 individual measurements. These cases were from almost entirely unselected material from our special prenatal clinic. This resulted in a larger variation than the percentile curves for biparietal diameter of other authors [Campbell and Newman]. However, these authors selected their material for "normal pregnancy" while we insured that neither "corrections" of the normal variation nor subjective criteria for exclusion have introduced a systematic error. The advantages of ultrasonography for monitoring of the pregnancy are self-evident: repeated examinations are possible, the examination takes little time, and the method is safe. The determination of the biparietal diameter for estimation of fetal development alone is insufficient because trunk measurements may indicate developmental disturbances (dystrophy and hypertrophy) before the growth of the biparietal diameter of the skull is affected. Furthermore, comparison of the fetal skull and trunk measurement may indicate errors in measurement or malformations (hydrocephalus, microcephalus). The following percentile curves are illustrated graphically: 1. Gestational age versus biparietal diameter (Fig. 1). 2. Biparietal diameter versus weeks of gestation (Fig. 2). 3. Length of gestation versus sagittal thoracic diameter (Fig. 3). 4. Length of gestation versus length of trunk (Fig. 4). 5. Sagittal thoracic diameter versus length of trunk (Fig. 5).