The etiology of Takayasu's arteritis is unknown; however, abnormality of the immune system plays an important role. To clarify a possible association between inflammatory diseases and Takayasu's arteritis, the authors retrospectively reviewed the medical records of 36 patients (2 men and 34 women), admitted to their department with this diagnosis. They found that 11 of the 36 patients had at least 1 other chronic or subacute inflammatory disease: Chronic tonsillitis, tuberculous lymphadenitis of the neck, chronic hepatitis B (infectious diseases); pyoderma gangrenosum, erythema nodosum (skin lesions); subacute thyroiditis, chronic thyroiditis (autoimmune diseases); Crohn disease, and ulcerative colitis (inflammatory diseases with unknown etiology). The present observation revealed a high prevalence of other inflammatory diseases in patients with Takayasu's arteritis and raises the possibility that Takayasu's arteritis may be associated with abnormality of the immune system activated by other inflammatory diseases, such as infection, autoimmune diseases, or inflammatory diseases of unknown origin.