Gastroesophageal reflux (GER) has been a suspected cause of infant deaths and sudden infant death syndrome (SIDS). We examined our 10-year experience with 499 consecutive infants 6 months of age or less who had extended (18 to 24 hours) esophageal pH monitoring performed to evaluate for GER. The data extracted from the esophageal pH records included the pH score, the pattern of GER (type I, II, or III), and the mean duration of reflux during sleep (ZMD). All infants were followed to determine the occurrence and cause of death during the first year of life. Of the 19 deaths found in the series, three were classified as SIDS and two were in-hospital deaths caused by reflux-induced aspiration. All five of these infants who died had a prolonged ZMD (greater than 3.8 minutes) and received either basic medical (n = 4) or no (n = 1) antireflux therapy. Four infants also had the type I pattern of GER. There was a 9.1% (4/44; 95% confidence limits, 2.5% to 21.7%) incidence of reflux-related or SIDS deaths in infants with type I GER and a prolonged ZMD who were treated nonoperatively, compared with none (0/83, P = .03) in the same group of infants treated with antireflux surgery. The incidence of SIDS was higher in infants with type I GER and a prolonged ZMD who were treated nonoperatively (3/44, 6.8%) compared with all other infants treated nonoperatively (0/265, 0%; P = .003).(ABSTRACT TRUNCATED AT 250 WORDS)