Based on centrally recorded data about all pregnancies that led to delivery in Sweden in the years from 1973 to 1981 this longitudinal study considers the course of pregnancies of all women who gave birth to their first three single babies during observation time especially regarding hypertension, proteinuria, pre-eclampsia and eclampsia-here subsumized under HP-disease. Incidence of HP-disease is shown to be 8.1% of all observed women, depending on the theoretical approach at a minimum of 34% and a maximum of 44% being due to primary, pregnancy-induced HP-disease. Some epidemiologic findings may give some hints on the etiology of HP-disease: In primary HP-disease mother's age is in the normal range, whereas infection of the urinary tract, diabetes mellitus, fetal deformity are found more frequently. Female fetus are over-represented with existence of HP-disease. The influence of HP-disease presence and parity on fetal development and fetal outcome are discussed.