OBJECTIVE It is unclear how gastro-oesophageal reflux disease (GORD) is diagnosed in primary care. The aim of this study is to compare patients given a diagnosis of GORD with those diagnosed with heartburn. METHODS Data from the UK General Practice Research Database were extracted for patients newly diagnosed with heartburn (n = 1841) or GORD (n = 5318) in 1996. METHODS Patient characteristics, morbidity, healthcare use and prescribed treatments were compared using unconditional logistic regression analysis. RESULTS GORD was diagnosed more frequently than heartburn (3.2 vs. 1.1 per 1000 patient-years). A diagnosis of GORD was less likely among females (odds ratio (OR): 0.8; confidence interval (CI): 0.7-0.9), smokers (OR: 0.8; CI: 0.7-0.9) and patients who consulted their physician frequently (OR: 0.8; CI: 0.7-0.9). There was a wide distribution in the ratio of GORD-to-heartburn diagnoses between primary care practices (mean 2.9; range 0-infinity). GORD patients were more likely to receive proton pump inhibitors (OR: 2.9; CI: 2.6-3.4), but 24% of GORD patients and 40% of heartburn patients received no acid-suppressive treatment in the month after diagnosis. CONCLUSIONS Several factors influenced the diagnosis of gastro-oesophageal reflux symptoms by primary care physicians. Further research is needed to aid the diagnosis of GORD in primary care.