Reninoma is a tumor of the renal juxtaglomerular cell apparatus that causes hypertension and hypokalemia via hypersecretion of renin. We describe a case of reninoma and provide a review of the literature, with a discussion emphasizing the diagnostic evaluation for such patients. The subject had persistent elevation of both plasma renin activity (PRA) and aldosterone. Imaging studies revealed the presence of a lesion in the renal cortex, which was further identified as a renin-producing lesion via selective venous catheterization following administration of an angiotensin-converting enzyme inhibitor (ACE-I). Following partial nephrectomy, the PRA and plasma aldosterone levels declined rapidly and the blood pressure and potassium supplementation requirements normalized. This case demonstrates the utility of both appropriate imaging studies and selective venous catheterization following provocative administration of an ACE-I for diagnosis.