Renal biopsy was performed in 125 patients with severe hypertension during pregnancy. Three groups could be defined: I: normal kidney; II: vascular lesions; III: nephropathy. The histological appearance could not be suspected from clinical criteria (age, parity, symptoms, date of appearance). About 70% of the patients in groups I and II had permanent metabolic disorders (mainly hypercholesterolemia) and had a familial history of hypertension. Recurrence of hypertension during subsequent pregnancies occurred in 70% of cases, identical in groups I and II, and therefore impossible to predict by histological findings. Permanent hypertension developed in 47% of group II patients and 8% of group I (p < 0.001). The authors conclude that hypertension during pregnancy affects a sub-population genetically selected and that renal biopsy is of little value for predicting the prognosis in future pregnancies. The indications for renal biopsy are discussed.