Contrast medium (CM)-induced nephropathy (CIN), defined as acute renal failure after administration of CM when alternative causes of renal damage have been excluded, is the third leading cause of acute renal injury necessitating hospitalization. However, the pathophysiology of CIN is complex and not fully understood. Gadolinium chelates, originally introduced as intravenous CM for magnetic resonance imaging and regarded as nonnephrotoxic, have been recommended to replace iodinated contrast agents in patients at risk for acute renal failure. Since then, some gadolinium-based CM have been reported to be associated with CIN, especially in patients with advanced renal disease. However, the biochemical and physicochemical properties of the gadolinium-chelates that are responsible for such nephrotoxicity have not been clearly defined, and the issue of gadolinium-induced nephrotoxicity remains controversial. This review surveys the literature with the purpose of clarifying the renal effects of gadolinium-based CM in patients with renal insufficiency.