Blood eosinophilia generally indicates an underlying allergic, infectious or hematologic disease. Corticoadrenal insufficiency is known to be another cause of blood eosinophilia. Eosinophilic cystitis is a rare disease in which the bladder wall is infiltrated by eosinophils; however, the etiology of eosinophilic cystitis remains unclear. We report a case of corticoadrenal insufficiency with blood eosinophilia developing gross hematuria and eosinophilic cystitis. The patient was treated with medical therapy, including oral corticosteroids, obtaining excellent results.