Diabetes mellitus is an important negative prognostic factor for mortality and morbidity in patients presenting with STEMI. About a quarter of patients presenting with STEMI are diabetic. These patients tend to be older and are more likely to have hypertension, dyslipidemia, higher BMI, pre-existing angina, heart failure, and history of CABG. This chapter covers the morbidity and mortality after STEMI in diabetic patients, thrombolysis in diabetic patients presenting with STEMI, medical management in diabetic patients presenting with STEMI, coronary angiography and primary percutaneous coronary intervention in STEMI in diabetic patients, atrial fibrillation in diabetic patients presenting with STEMI, diagnosis of diabetes mellitus at presentation with STEMI, influence of gender on prognostication of STEMI in diabetes.