BACKGROUND: Chest pain is an initial symptom for several minor diseases but acute myocardial infarction (AMI) should not be missed. AIM: To assess the influence of initial diagnosis and degree of certainty of this initial diagnosis on the referral decision and the referral method (urgent-non-urgent) in patients contacting their GP with chest pain. STUDY DESIGN: Observational study. SETTING: The study was performed in a sentinel network of general practices in Belgium, covering almost 1.6% of the population. SUBJECTS: All patients attending their GP and complaining of chest pain during 2003. METHOD: The relationships were reported as proportions and in odds ratios (OR) with their 95% confidence intervals. RESULTS: 1996 patients were included (men 52%). Men were referred more often (OR = 1.44; 95% CI: 1.13-1.82). Age shows no relation to referral (OR = 1.06; 95% CI: 0.83-1.35) but predicts urgent referral (OR = 1.46; 95% CI: 1.02-2.08). Odds ratios in case of serious heart disease were high with 11.58 (95% CI: 5.72-23.44) when the GP was certain of his diagnosis and 2.96 (95% CI: 1.59-5.51) if not. If the GP was uncertain, in all disease categories 54% (95% CI: 48-59) of the patients were referred non-urgently. CONCLUSION: Referral rates for patients with chest pain were influenced by the initial diagnosis and the degree of certainty of this initial diagnosis.