Two gastroesophageal reflux disease (GERD) symptom questionnaires were developed and tested prospectively in a pilot study conducted in infants (1 through 11 months) and young children (1 through 4 years) with and without a clinical diagnosis of GERD. A pediatric gastroenterologist made the clinical diagnosis of GERD. Parents or guardians at 4 study sites completed the questionnaires, providing information on the frequency and severity of symptoms appropriate to the 2 age cohorts. In infants, symptoms assessed were back arching, choking or gagging, hiccups, irritability, refusal to feed and vomiting or regurgitation. In young children, symptoms assessed were abdominal pain, burping or belching, choking when eating, difficulty swallowing, refusal to eat and vomiting or regurgitation. Respondents were asked to describe additional symptoms. Symptom frequency was the number of occurrences of each symptom in the 7 days before completion of the questionnaire. Symptom severity was rated from 1 (not at all severe) to 7 (most severe). An individual symptom score was calculated as the product of symptom frequency and severity scores. The composite symptom score was the sum of the individual symptom scores. The mean composite symptom and individual symptom scores were higher in infants (P<0.001 and P<0.05, respectively) and young children (P<0.001 and P<0.05, respectively) with GERD than controls. Vomiting/regurgitation was particularly prevalent in infants with GERD (90%). Both groups with GERD were more likely to experience greater severity of symptoms. We found the GERD Symptom Questionnaire useful in distinguishing infants and young children with symptomatic GERD from healthy children.