The author describes a case of early onset of asymptomatic renal insufficiency in a young patient with ulcerative colitis, treated by large doses of mesalazine. After discontinuation of the drug rapid restoration of renal functions occurred. Contrary to all hitherto published cases, this pati- ent developed renal failure very soon. Urea serum levels reached pathological values after 27 days and the creatinine level already 15 days after the onset of mesalazine administration. The renal affection was unequivocally confirmed by examination of the urine (semiquantitative and quanti- tative) and dynamic functional scintigraphy.

        Key words: 5-aminosalicylic acid - Mesalazine - Renal insufficiency - Tubulointerstitial nephritis -