With the possible exception of a unique glomerular lesion, the morphological changes in patients dying with convulsions, coma, and other complications of acute hypertension are not specific for a pathological entity initiated by aberrations peculiar to the pregnant state. Renal biopsies afford a means for classifying pregnant patients with acute hypertension. The glomerular lesion, believed to be pathognomonic of preeclampsia, was not found in 25% of 63 primiparas who fulfilled the clinical criteria for preeclampsia; chronic renal disease was present without the toxemic lesion in 30% of 214 pregnant patients with acute hypertension. These findings suggest that chronic renal disease plays a more important role in the acute hypertension of pregnancy than current statistics indicate, and that data pertaining to the hypertensive disorders of pregnancy must be interpreted with caution when their differentiation is based upon clinical criteria alone.