Tracheal bronchus is an aberrant bronchus that arises most often from the right tracheal bronchial wall above the carina and is the result of an additional tracheal outgrowth early in embryonic life. Its incidence ranges from 0.1 to 5%. This anomaly is usually diagnosed incidentally during bronchoscopy or bronchography in patients with various respiratory problems. Tracheal bronchus may be associated with other bronchopulmonary anomalies such as tracheal stenosis, pulmonary agenesis, pulmonary sequestration, abnormal lobulation, and Down's syndrome. In patients without specific clinical symptoms, a incidentally diagnosed tracheal bronchus does not require any treatment. We report a case of 59-year-old man incidentally detected accessory tracheal bronchus associated with bronchial asthma with review of literatures.