The Alpha Omega Cohort is a prospective study of 4,837 state-of-the-art drug-treated Dutch patients aged 60-80 years who had a clinically diagnosed myocardial infarction up to 10 years before enrolment. During the first 40 months of follow-up, patients took part in an experimental study of low doses n-3 fatty acids (Alpha Omega Trial, ClinicalTrials.gov NCT00127452). At baseline (2002-2006), data on medical history, medication use, diet, lifestyle and other factors were collected by means of questionnaires. Patients were physically examined by trained research nurses and blood samples were obtained. Follow-up for vital status and cause-specific mortality is ongoing. The trial was approved by a central medical ethics committee (Haga Hospital, The Hague, The Netherlands) and all patients provided written informed consent.