A system of estimating intrauterine size by adding the maximal longitudinal and transverse uterine areas (LTUA) is described. In our hands this measurement is less prone to observer variability and more sensitive in diagnosing intrauterine growth retardation (IUGR) than the total intrauterine volume (TIUV) measurement. Intraobserver variability for the LTUA was 3.7 per cent, whereas that for the TIUV was 10.0 per cent. Interobserver variability was 6.5 per cent for the LTUA and 12.9 per cent for the TIUV. Sensitivity for the LTUA and the TIUV was 70 per cent and 40 per cent, respectively, and the respective specificities were 94 per cent and 96 per cent. These results suggest that the LTUA may be a more accurate and reliable method of predicting IUGR than is the TIUV.