The purposes of this study were 1) to determine the prognosis of silent ischemia in an unselected group of patients referred for exercise testing, and 2) to assess whether age or the presence of myocardial infarction or diabetes mellitus influences the prevalence of silent myocardial ischemia during exercise testing. The design was retrospective, with a 2 year mean follow-up period. The study group consisted of 1,747 predominantly male in-patients and outpatients referred for exercise testing at a 1,200 bed Veterans Administration hospital. The main result was that the mortality rate was significantly greater (p = 0.02) among patients with abnormal ST segment depression than in patients without ST depression. The presence or absence of angina pectoris during exercise testing was not significantly related to death. The prevalence of silent ischemia was not significantly different among patients categorized according to myocardial infarction or diabetes mellitus status, but was directly related to age. It is concluded that, in patients with an ischemic ST response to exercise testing, the presence or absence of angina pectoris during the test does not alter the risk of death. The prevalence of silent ischemia during exercise testing is not statistically different among patients with recent, past or no myocardial infarction or with insulin-dependent or noninsulin-dependent diabetes mellitus.