In the years 1969 - 1973, 0.3% of 17000 unselected non-diabetic pregnancies were complicated by severe pre-eclampsia, 0.6% by mild pre-eclampsia and 0.6% by hypertension in pregnancy. Records from affiliated maternity centers and the hospital were studied for these 261 women and for 260 women with matched normotensive pregnancies. The women with pre-eclampsia/hypertension in pregnancy had higher blood pressure than the control group very early in pregnancy. The hypertensive women were more often primiparous and they had a slightly higher body weight. The patients with severe pre-eclampsia were older than the other women (30.4 vs 25.4 years for controls, p less than 0.001). Immigrants were not more commonly found in the hypertensive groups, but unmarried mothers were more often seen in the mild pre-eclampsia and pregnancy hypertension groups, 19.1% and 20.6% respectively compared to 7.7% in the control group (p less than 0.01). A family history of hypertension was frequently reported in all groups. The most striking characteristic of women with pre-eclampsia/hypertension in pregnancy was their elevated blood pressure before or very early in pregnancy.