For 2,058 consecutive patients hospitalized for suspected acute myocardial infarction (AMI) but in whom AMI was later ruled out, we describe the prognosis with particular emphasis on diabetics. In all, a previous history of diabetes mellitus occurred in 290 (14%) of the patients. Compared with nondiabetics, they had a longer delay time between onset of symptoms and arrival in hospital. During 1 year of follow-up, their mortality rate was 28% compared with 14% for nondiabetics (p < 0.001), and their reinfarction rate was 20% compared with 10% for nondiabetics. More diabetics died in association with a fatal myocardial infarction and more frequently had ventricular fibrillation preceding death. With the exception of re-infarction, no clear difference in terms of morbidity was observed between the two groups. We conclude that the prognosis in diabetics in whom AMI is ruled out is poor, with between one-quarter and one-third not surviving 1 year.