IMPORTANCE: Coronary artery disease (CAD) is a major cause of cardiovascular morbidity and mortality in patients with diabetes mellitus, yet CAD often is asymptomatic prior to myocardial infarction (MI) and coronary death. OBJECTIVE: To assess whether routine screening for CAD by coronary computed tomography angiography (CCTA) in patients with type 1 or type 2 diabetes deemed to be at high cardiac risk followed by CCTA-directed therapy would reduce the risk of death and nonfatal coronary outcomes. DESIGN, SETTING, AND PARTICIPANTS: The FACTOR-64 study was a randomized clinical trial in which 900 patients with type 1 or type 2 diabetes of at least 3 to 5 years' duration and without symptoms of CAD were recruited from 45 clinics and practices of a single health system (Intermountain Healthcare, Utah), enrolled at a single-site coordinating center, and randomly assigned to CAD screening with CCTA (n = 452) or to standard national guidelines-based optimal diabetes care (n = 448) (targets: glycated hemoglobin level <7.0%, low-density lipoprotein cholesterol level <100 mg/dL, systolic blood pressure <130 mm Hg). All CCTA imaging was performed at the coordinating center. Standard therapy or aggressive therapy (targets: glycated hemoglobin level <6.0%, low-density lipoprotein cholesterol level <70 mg/dL, high-density lipoprotein cholesterol level >50 mg/dL [women] or >40 mg/dL [men], triglycerides level <150 mg/dL, systolic blood pressure <120 mm Hg), or aggressive therapy with invasive coronary angiography, was recommended based on CCTA findings. Enrollment occurred between July 2007 and May 2013, and follow-up extended to August 2014. MAIN OUTCOMES AND MEASURES: The primary outcome was a composite of all-cause mortality, nonfatal MI, or unstable angina requiring hospitalization; the secondary outcome was ischemic major adverse cardiovascular events (composite of CAD death, nonfatal MI, or unstable angina). RESULTS: At a mean follow-up time of 4.0 (SD, 1.7) years, the primary outcome event rates were not significantly different between the CCTA and the control groups (6.2% [28 events] vs 7.6% [34 events]; hazard ratio, 0.80 [95% CI, 0.49-1.32]; P = .38). The incidence of the composite secondary end point of ischemic major adverse cardiovascular events also did not differ between groups (4.4% [20 events] vs 3.8% [17 events]; hazard ratio, 1.15 [95% CI, 0.60-2.19]; P = .68). CONCLUSIONS AND RELEVANCE: Among asymptomatic patients with type 1 or type 2 diabetes, use of CCTA to screen for CAD did not reduce the composite rate of all-cause mortality, nonfatal MI, or unstable angina requiring hospitalization at 4 years. These findings do not support CCTA screening in this population. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT00488033.