We describe a patient with IgA nephropathy associated with Crohn disease. IgA nephropathy first appeared at the age of 10 years. Combined therapy with prednisolone, cyclophosphamide, warfarin, and angiotensin-converting enzyme inhibitor resulted in clinical improvement over the following year, and remission was maintained. At the age of 13 years, the patient developed Crohn disease and IgA nephropathy recurred. Significant increases in serum IgA were associated with progression of Crohn disease. An elemental diet combined with oral prednisolone resulted in clinical improvement of Crohn disease and in remission of nephropathy and normalization of serum IgA concentration. The clinical course of the two diseases was linked, suggesting a common pathogenetic mechanism involving an IgA immune response to mucosal challenge in the intestine.