We assessed the association of BMI with all cause and cardiovascular (CV) mortality in a contemporary acute coronary syndrome (ACS) cohort. Patients from the Australian Cooperative National Registry of Acute Coronary Care, Guideline Adherence and Clinical Events (CONCORDANCE) between 2009 – 2019, were divided into BMI sub-groups (underweight: <18.5, healthy: 18.5-25, overweight: 25.1-30, obese 4: >30). Logistic regression was used to determine the association between BMI group and outcomes of all cause and CV death in hospital, and at 6months. 8503 patients were identified, mean age 64±13, 72% male. The BMI breakdown was: underweight- 95, healthy- 2140, overweight- 3258, obese- 3010. Underweight patients were more likely to be female (61% vs 32% p<0.0001) with less diabetes (12% vs 18% p=0.02). Obese patients were younger (66±12 vs 67±13), with more hypertension, diabetes and dyslipidemia vs healthy (all p<0.05). There was no difference in hospital mortality between underweight and healthy while obese had lower hospital mortality than healthy: all cause: 1% vs 4%, aOR 0.49 (0.27, 0.87); CV: 1% vs 3%, 0.51 (0.27, 0.96). At 6-months underweight had higher mortality than healthy: all cause: 11% vs 4%, 2.69 (1.26, 5.76); CV: 7% vs 1%, 3.54 (1.19, 10.54); while obese had lower mortality: all cause: 1% vs 4%, 0.48 (0.29, 0.77); CV: 0.4% vs 1%, 0.42 (0.19, 0.93). BMI is associated with mortality following an ACS. Underweight patients have the worst outcomes and obese the best, consistent with ‘persistence of the obesity paradox in this cohort.