Survival rates for infants undergoing surgical repair of oesophageal atresia with tracheo-oesophageal fistula (OA-TOF) have improved dramatically, but this condition remains associated with substantial morbidity. Most studies of patients following OA-TOF repair have concentrated on school-age and older people; whereas, the most hazardous period is infancy. We aimed to assess respiratory function in a group of infants following primary operative repair, and to relate the results to clinical findings during the first year of life. We studied 16 infants within 3 months of primary repair of OA-TOF. Measurements were made of maximum expiratory flow at functional residual capacity (VmaxFRC), thoracic gas volume (TGV) and airways resistance (Raw). Ten infants had tests repeated, usually to assess progress alongside continuing symptoms, or to ascertain improvement following additional surgery. Seven infants had essentially normal initial respiratory function tests, and six remained either symptom-free or developed only minor clinical problems. One infant subsequently developed stridor, with spontaneous improvement towards the end of the first year. The remaining nine infants had abnormal initial respiratory function tests: one was symptom-free at that time. The remainder developed respiratory and/or gastro-oesophageal symptoms. The functional abnormalities appeared to reflect the severity of the clinical problems encountered. We conclude that respiratory function testing in infants following OA-TOF repair may augment the value of clinical appraisal, help define postoperative respiratory status, and provide a general guide to likely clinical progress.