A 24 year-old woman had a congenital solitary kidney with renovascular hypertension due to fibromuscular dysplasia. She had been treated as having essential hypertension until she developed preeclampsia and HELLP (hemolysis, elevated liver enzymes, and low platelet count) syndrome at 28 weeks of gestation. Plasma renin activity and captopril test results did not indicate any abnormalities. However, renography revealed captopril-induced deterioration. Magnetic resonance angiography was also useful to detect renal artery stenosis. These findings were confirmed by renal angiography. After successful percutaneous transluminal renal angioplasty, her blood pressure and the pattern of captopril renography normalized.