A 47-year-old woman presented with a 2-month history of generalized arthralgia and a 10-day history of oral aphthous ulcers. After hospitalization, papulopustular lesions and perianal ulcerations developed. Pathergy test was positive and ophthalmological examination was normal. The presence of oral aphthous ulcers, genital ulcerations, papulopustular lesions and arthralgia, and the positive pathergy test suggested the diagnosis of Behçet's disease (BD). In a few days, positive pathergy reactions and papulopustular lesions evolved into bullous lesions, which were diagnosed dermatopathologically as pyoderma gangrenosum. Two days after the presentation of papulopustular lesions, the patient experienced diarrhoea accompanied by bloody stools and mucus. Histopathological examination of biopsy specimens showed no vasculitis but revealed findings suggestive of Crohn's disease. The patient responded well to treatment with systemic steroids and 5-aminosalicylic acid. Our case demonstrates that the differential diagnosis of BD and inflammatory bowel disease may be perplexing and that these two diseases may be closely related.