To determine the preferred investigation of congenital vascular compression of the trachea, preoperative investigation in 40 patients undergoing surgery 1981-91 was analysed. The importance of preoperative identification of detailed arterial anatomy in determining surgical technique was also assessed in 122 consecutive patients undergoing surgery 1952-91. Of the 40 patients (median age 5 months) seen 1981-91, barium swallow before referral suggested the diagnosis of vascular compression in 26 of 27 (96%). Angiography (1/3), bronchoscopy (0/6), and echocardiography (2/6) were generally unhelpful in diagnosing vascular compression before referral. Echocardiography was performed after referral in 18 consecutive patients since 1986 and the correct arterial anatomy was identified in 16 (88%); hyperinflation resulted in inadequate images in the two others. Barium swallow is the investigation of choice to screen for suspected vascular compression of the trachea; echocardiography at the referral centre can define the arterial anatomy in nearly all patients. Further investigation can be reserved for selected cases.