The package inserts for products containing 5-aminosalicylic acid, or mesalamine, include the following language regarding the risk of adverse kidney effects: "renal impairment, including minimal change nephropathy, acute and chronic interstitial nephritis, and rarely renal failure, has been reported in patients given products such as mesalamine delayed-release tablets that contain mesalamine or are converted to mesalamine." In this article, we review the data regarding this nephrotoxicity and the recommendations regarding appropriate monitoring. Chronic interstitial nephritis is a rare occurrence in patients treated with these drugs for Crohn disease and ulcerative colitis. Patients often present with asymptomatic reductions in glomerular filtration rate, without accompanying pyuria, skin lesions, or eosinophilia, unlike cases of acute interstitial nephritis. Drug cessation is usually associated with improved kidney function. However, if left undetected, more prolonged exposure to the drug can lead to irreversible kidney failure and end-stage kidney disease. No convincing studies demonstrate efficacy of treatment with corticosteroids. Frequent monitoring of serum creatinine, especially in the first years after initiation of therapy, is recommended.