Growing evidence was collected that non-alcoholic liver fatty disease (NAFLD) is a risk factor for coronary atherosclerosis in terms of angiographic appearance, but its involvement in acute coronary syndromes is still debated. We investigated the prevalence and severity of NAFLD in non-diabetic patients admitted for ST-segment elevation myocardial infarction (STEMI) and its association with multi-vessel coronary artery disease (CAD). Ninety-five consecutive non-diabetic patients admitted to cardiac ICU for STEMI were studied by ultrasound within 72 h from admission. NAFLD was graded according to a semi-quantitative severity score as mild (score < 3) or moderate-severe (> 3 score). Prevalence of cardiovascular (CV) risk factors, atherosclerotic burden markers and metabolic syndrome (MS) was investigated. The overall prevalence of NAFLD was 87%. Forty-eight patients showed moderate-severe NAFLD (SFLD). Thirty-five patients showed mild NAFLD (MLFD group) and 12 patients had no NAFLD. Patients with SFLD were younger and showed higher prevalence of multi-vessel CAD (i.e. > 2) than patients with mild MFLD (P < 0·01). Total cholesterol, triglycerides, body mass index and waist circumference were higher and HDL lower in SFLD than MFLD patients. About 50% of all NAFLD patients did not have MS. MS prevalence was higher in SFLD than MLFD patients (P < 0·05) and among MS components, waist circumference and triglyceride levels showed the strongest association with SFLD (P < 0·05). At logistic regression analysis, SFLD was independently associated with a three-fold risk of multi-vessel CAD. In non-diabetic patients admitted for STEMI NAFLD prevalence was very high. Severe NAFLD independently increased the risk for multi-vessel CAD associated to CV events.