Uterine artery blood flow velocity waveforms (FVW) were recorded longitudinally in 41 women with undisturbed pregnancy as well as in 32 women with complicated pregnancy at 4-week intervals from a gestational age of 18 weeks onwards. Of these women, four did not complete the study. In a second group of 76 patients at least one FVW was recorded after admission to the obstetrical department because of complicated pregnancy. The Pulsatility-Index (PI) for normal pregnancy was based on the results of the 41 women with undisturbed pregnancy (Mulders et al. (1988) Early Hum. Dev., 17, 55-70). The complete study group (n = 145) was divided in two groups, based on the value of the last measured uterine artery PI before delivery in the abnormal PI group (PI greater than or equal to 1.02 before 32 weeks or PI greater than or equal to 0.91 after 32 weeks, n = 38) hypertension, fetal distress during pregnancy, premature delivery, small for gestational age babies (SGA) and lower placental weight were all significantly increased. In each of the groups of patients with either SGA, fetal distress during pregnancy, pre-existing hypertension with proteinuria and pregnancy-induced hypertension with or without proteinuria the mean PI was significantly increased as compared to the results in normal pregnancy. Sensitivity and specificity of the last uterine artery PI for the detection of SGA and/or fetal distress during pregnancy were 48.8% and 82.7%, respectively. The longitudinally studied women (n = 73) were divided in two groups, based on uterine artery PI before 32 weeks of gestation; in the abnormal PI group (PI greater than or equal to 1.02, n = 12) pregnancy was more complicated by premature delivery and low birth weight. Sensitivity for the early prediction of pathological pregnancies (at least one pathological phenomenon as mentioned above) was 30.4%, whereas specificity was 90.0%.