Five months after heart-lung transplantation for treatment of end-stage cystic fibrosis, a 14-year-old girl had a swelling over the manubrium that was identified as a pseudoaneurysm at the aortic anastomotic site by means of cross-sectional echocardiography with color flow Doppler mapping. The diagnosis was confirmed at operation, despite which she died. Biopsy material taken during the operation revealed chronic sternal osteomyelitis caused by Pseudomonas aeruginosa. Disruption of the aortic anastomosis by infection may be a major complication of heart-lung transplantation for treatment of cystic fibrosis.