Gastroesophageal reflux (GER) is common after repair of esophageal atresia with a distal tracheoesophageal fistula (EATOF). In a retrospective study we assessed whether early 18-h pH monitoring can predict the development of EATOF-associated gastroesophageal reflux. During 1980-1997, 90 consecutive patients had primary repair for EATOF. Development of GER was classified as favorable if the patient developed no esophagitis or mild esophagitis and needed no antireflux medication, and as unfavorable if the patient developed moderate or secondary esophagitis or required an antireflux procedure. Patients who developed unfavorable GER outcome before pH monitoring or needed secondary reconstruction or those whose endoscopic follow-up data were insufficient were excluded. Eighteen-hour pH monitoring was considered pathologic if esophageal pH was <4 more than 10% of the recorded time or 5% of the recorded time minus 2 h after each meal, or if there were more than three preprandial reflux periods lasting longer than 5 min. A total of fifty patients were included into the study. pH monitoring was performed at the median age of 9.2 (range 2.5-95.0) months and classified as pathologic in 10 and normal in 40 patients. After a median follow-up of 59 (0.3-217.6) months, nine of 10 (90%) patients with pathologic pH monitoring and five of 40 (12.5%) patients with normal pH monitoring developed unfavorable outcomes ( p<.05). We conclude that early pH monitoring predicts the development of significant GER, but because 12.5% of patients with normal early pH monitoring also developed significant GER, early pH monitoring alone does not rule out the development of significant GER.