This is a report of a retrospective study of the effects of preexisting glomerular disease and pregnancy on each other. Two hundred forty pregnancies in 166 Japanese women who delivered between 1970 and 1988 were analyzed. There were 206 (86%) live births, 14 (6%) perinatal deaths, and 20 (8%) spontaneous abortions. Perinatal loss was greatest In women with hypertension and/or glomerular filtration rate (GFR) less than 70 mLlmin before conception. Pregnancy did not appear to adversely affect the underlying glomerular disease if GFR was greater than 70 mLlmln and blood pressure. was below 140/90 mm Hg. However, with moderately impaired renal function (creatinine > 124 μmol/L [1.4 mg/dL] or GFR < 50 mL/min), the long-term prognosis was poorer, despite generally favorable obstetrical outcomes. Gravidas with membranoproliferative glomerulonephritis had the highest rates of hypertension (29%) and decreased renal function (33%) at final follow-up, ie, the type and severity of glomerulonephritis had a major Impact on clinical course. © 1991, National Kidney Foundation, Inc.. All rights reserved.