Three patients are described in whom renal cell carcinoma was diagnosed between seven months and 14 years after the onset of ulcerative colitis. All three had required treatment with corticosteroids and azathioprine, as well as maintenance therapy with 5-aminosalicylate derivatives, for chronic active colitis. One patient had coexisting polymyalgia rheumatica; one had primary biliary cirrhosis. It is uncertain whether this association, which has not previously been described, has pathogenetic importance or has arisen simply by chance. Genetic predisposition or the effect of drug treatment, particularly immunosuppression, may be pertinent to the co-occurrence of these diseases.