The association between respiratory complications of gastroesophageal reflux (GER) and prematurity in infants has not been described completely. We studied 82 consecutive infants less than 6 months of age with major respiratory symptoms suspected to be caused by GER. Twenty-eight patients had bronchopulmonary dysplasia (BPD). Extended (18 to 24 hours) esophageal pH monitoring was used to document GER with a pH score. Respiratory complications were considered to be caused by GER if a prolonged mean duration of sleep reflux (ZMD) was found. Seventy-five of the 82 (91%) infants had documented GER, but only 45 (55%) had a prolonged ZMD. The incidence of GER was high regardless of the gestational age at birth, postconceptual age at time of study, and the presence of BPD. The incidence of a prolonged ZMD was higher in infants who were 34 to 39 weeks' gestation (10/12, 83%) than in infants who were less than 34 weeks' gestation at birth (15/37, 41%; P = .01). The incidence of a prolonged ZMD was lowest in infants 39 weeks or less postconceptual age at the time of study (4/14, 29%; P = .017). Most infants with BPD did not have a prolonged ZMD (12/28, 43%). However, 11 of the 12 (92%) infants with BPD and a prolonged ZMD showed dramatic improvement after effective antireflux therapy compared with 0 of 16 infants with BPD and normal ZMD (P less than .001).(ABSTRACT TRUNCATED AT 250 WORDS)