OBJECTIVE--To test whether a fat reduced diet rich in soluble dietary fibre, antioxidant vitamins, and minerals reduces complications and mortality after acute myocardial infarction. DESIGN--Randomised, single blind, controlled trial. SETTING--Primary and secondary care research centre for patients with myocardial infarction. SUBJECTS--505 patients with suspected acute myocardial infarction. Those with definite or possible acute myocardial infarction and unstable angina based on World Health Organisation criteria were assigned to diet A (n = 204) or diet B (n = 202) within 24-48 hours of infarction. INTERVENTIONS--Both groups were advised to follow a fat reduced diet. Group A was also advised to eat more fruit, vegetables, nuts, and grain products. MAIN OUTCOME MEASURES--Mortality from cardiac disease and other causes. Serum lipid concentrations and compliance with diet. RESULTS--Blood lipoprotein concentrations and body weight fell significantly in patients in group A compared with those in group B (cholesterol fell by 0.74 mmol/l in group A v 0.32 mmol/l in group B, 95% confidence interval of difference 0.14 to 0.70, and weight by 7.1 v 3.0 kg, 0.52 to 7.68). The incidence of cardiac events was significantly lower in group A than group B (50 v 82 patients, p less than 0.001). Group A also had lower total mortality (21 v 38 died, p less than 0.01) than group B. CONCLUSIONS--Comprehensive dietary changes in conjunction with weight loss immediately after acute myocardial infarction may modulate blood lipoproteins and significantly reduce complications and mortality after one year.