Incidence figures for hypertensive disease in pregnancy (HDP) vary widely in epidemiological studies due to variations in definitions, the occurrence of risk factors and differing methods of data collection. In Uppsala county all pregnant women with a diastolic blood pressure of 90 mmHg or more were prospectively registered within a 2-year-period. The incidence of hypertension noted in the antenatal clinics was found to be 7.2%. In 56% of the cases hypertension was first noted after 37 weeks of gestation. The group of patients presenting before term with hypertension not normalized by bed rest in hospital and without complicating factors was only 14% of the whole material. The implications of the findings for discussions on therapy and complications in HDP are discussed.