OBJECTIVE The objectives of this study were to investigate the prevalence of posttraumatic stress disorder in patients with a first myocardial infarction compared with a random sample of healthy controls and to determine variables associated with the disorder. METHODS A questionnaire was distributed to 112 consecutive patients 4 to 6 weeks after infarction and to 115 healthy controls selected randomly from the general population. Objective clinical measures were obtained from the patients' medical records. RESULTS Twenty-five (22%) patients qualified for a diagnosis of posttraumatic stress disorder (PTSD) compared with 8 (7%) controls with patients being more than a three-fold (OR: 3.84; 95% CI: 1.65 to 8.94) risk of having the disorder. When adjusting for other variables, the risk was reduced to above a two-fold risk (OR: 2.71; 95% CI: 0.99-7.41). In patients and controls, depression and neuroticism were associated with a diagnosis of PTSD adjusting for other variables. In patients, anxiety was associated with a diagnosis of PTSD adjusting for other variables. Left ventricular ejection fraction and symptoms of angina pectoris were not related to a diagnosis of PTSD in the patient group. CONCLUSIONS Given that previous research has shown that persons with PTSD are at increased risk of cardiovascular diseases, cardiac patients with the disorder may be at a higher risk of recurrent cardiac events. Although longitudinal studies are needed to confirm such a relationship, this disorder should not be overlooked because of its potential role in reinfarctions and mortality.