AIM: To validate the gastrointestinal symptom score as an outcome measure for functional dyspepsia. METHODS: In focus groups, 10 dyspepsia-specific items including nausea, sickness, vomiting, bloating, abdominal cramps, early satiety, acidic eructation/heartburn, loss of appetite, retrosternal discomfort, epigastric pain/upper abdominal pain were identified. Ninety-five patients with functional dyspepsia and 56 healthy controls were recruited and responsiveness evaluated by analysing gastrointestinal symptom score data from 357 patients from previous placebo-controlled trials. Gastrointestinal symptom score response data were correlated with the patient's global assessments of efficacy. Convergent validity was assessed by correlating the gastrointestinal symptom score with the results obtained by the Nepean Dyspepsia Index. RESULTS: Sensitivity: In patients and healthy controls gastrointestinal symptom score yielded consistently different scores (all P < 0.0001). TEST-RETEST RELIABILITY: Gastrointestinal symptom score determined at the two time points were significantly correlated (r-values ranging from 0.842 to 0.901). CONVERGENCE VALIDITY: Gastrointestinal symptom score of both rating groups were significantly correlated with the symptom-specific component of the Nepean Dyspepsia Index (r-vales ranging from 0.666 to 0.764, P < 0.01). RESPONSIVENESS: Responses of gastrointestinal symptom score during treatment were different for patients with a global self assessment as responders compared with non-responders (all P < 0.0055). CONCLUSION: The gastrointestinal symptom score is a valid and reliable instrument to assess symptom intensities in patients with functional dyspepsia.