Diabetes mellitus (DM) is associated with more extensive coronary atherosclerosis and more vulnerable plaque phenotypes. However, DM should not be considered a homogeneous and purely binary entity in terms of risk assessment. We evaluated the impact of prediabetic status on coronary atherosclerosis burden in patients with first-time acute coronary syndrome (ACS) who underwent urgent coronary angiography. The patients were divided into DM, prediabetes, and control groups. The 3-vessel disease (TVD) rates and SYNTAX and Gensini scoring systems for defining atherosclerotic burden were compared. The study was conducted in 469 consecutive patients admitted with a diagnosis of ACS. Of these, 250 patients were admitted at the first occurrence of ACS undergoing diagnostic coronary angiography. SYNTAX and Gensini scores and TVD rates were higher in prediabetic patients than in nondiabetic patients (P =.004, P =.008, and P =.014, respectively), but similar in prediabetic and diabetic patients (P =.912, P =.773, and P = 1.000, respectively). Coronary atherosclerosis burden is more advanced in prediabetic patients than in nondiabetic patients and is comparable between prediabetic and diabetic patients at first presentation of ACS. Cardiologists should not miss the opportunity to diagnose prediabetes and DM when patients present with an ACS.