Two cases of traumatic paramediastinal air cyst are presented with a review of the literature. This rare condition affects young people and usually occurs on the left side of the chest. Its course is spontaneously benign. Although they are usually easily diagnosed on chest roentgenograms, these cysts may sometimes be difficult to differentiate from other more serious traumatic lesions. Computed tomography (or a contrast swallow roentgenogram in some instances) can elucidate doubtful cases.