A 44-year-old man with a 17-year history of Crohn's disease (CD) was referred to our nephrology department on suspicion of drug-induced nephrotoxicity. Over the preceding 18 months, he had slowly progressive renal insufficiency with slight urinary abnormalities. His disease activity had been well controlled up to that point with 5-aminosalicylic acid and azathiopurine. Laboratory examination revealed slight proteinuria without hematuria and an elevated serum creatinine level of 1.4 mg/dl. Pathological examination revealed amyloid A (AA) deposition in the kidney, predominantly in the arterial and arteriolar walls with little to none in the glomerular capillaries. AA amyloidosis is typically accompanied by glomerular amyloid deposition and massive proteinuria. In the present case, however, vascular amyloid deposition was predominant, and the renal function was deteriorated with slight urinary abnormalities. The present case confirmed the importance of conducting a definitive pathological diagnosis of renal insufficiency in CD patients.