Partial duplication of the trachea is a very rare congenital tracheal anomaly that is detected during infancy. To our knowledge, there are only 3 reported cases of partial duplication of the trachea in the literature, which were all detected during infancy. We are reporting the first case of partial duplication of the trachea in an adult, which was detected accidentally during routine diagnostic bronchoscopy. Partial duplication of the trachea can easily be misdiagnosed as an accessory bronchus or congenital tracheal diverticulum, if it is not carefully evaluated. It is possible that similar cases in the past may have been misdiagnosed as tracheal bronchus or congenital tracheal diverticulum on bronchoscopy.