BACKGROUND Myocardial infarction (MI) is associated with an increased risk of anxiety, depression, low quality of life, and all-cause mortality. Whether MI is associated with an increased risk of suicide is unknown. We examined the association between MI and suicide. RESULTS We conducted a population-based case-control study by retrieving data from 5 nationwide longitudinal registers in Denmark. As cases, we selected all persons aged 40 to 89 years who died by suicide from 1981 to 2006. As controls, we randomly selected up to 10 persons per case matched by sex, day of birth, and calendar time. We identified 19,857 persons who committed suicide and 190,058 controls. MI was associated with a marked increased risk of suicide. The risk of suicide was highest during the first month after discharge for MI for patients with no history of psychiatric illness (adjusted rate ratio, 3.25; 95% confidence interval, 1.61 to 6.56) and for patients with a history of psychiatric illness (adjusted rate ratio, 64.05; 95% confidence interval, 13.36 to 307.06) compared with those with no history of MI or psychiatric illness. However, the risk remained high for at least 5 years after MI. CONCLUSIONS MI is followed by an increased risk of suicide for persons with and without psychiatric illness. Our results suggest the importance of screening patients with MI for depression and suicidal ideation.