OBJECTIVES: To evaluate the prevalence, characteristics, and in-hospital outcomes of metabolic syndrome (MS) in acute coronary syndrome (ACS) patients in Oman. METHODS: Data were analyzed from 1,392 consecutive patients admitted to 15 hospitals throughout Oman with the final diagnosis of ACS during May 8, 2006 to June 6, 2006 and January 29, 2007 to June 29, 2007, as part of Gulf RACE (Registry of Acute Coronary Events). MS was defined, as stipulated by the recent ATP-III guidelines, as having 3 or more of the following abnormalities: waist circumference of  ≥94cm for men and ≥80cm for women, high triglyceride levels (of ≥150mg/dL (1.7mmol/L) or drug treatment), low high density lipoprotein cholesterol (HDL-C) levels (of <40mg/dL (1.0 mmol/L) for men and <50mg/dL (1.3 mmol/L) for females or drug treatment), blood pressure (of ≥130 mmHg for systolic and/or ≥85 mmHg for diastolic or drug treatment), and blood sugar (of ≥100 mg/dL (≥5.6 mmol/L) or drug treatment). RESULTS: The overall prevalence rate of MS in ACS patients in Oman was 66% with females being the majority (80% versus 57%; p<0.001). MS was associated with higher median body mass index scores (27 versus 24; p<0.001), diabetics (45% versus 19%; p<0.001), hyperlipidemia (40% versus 23%; p<0.001), hypertension (62% versus 34%; p<0.001), renal impairment (9.3% versus 3.4%; p<0.001), killip score >II (13% versus 8%; p=0.004) and non-ST segment elevation myocardial infarction (78% versus 68%; p<0.001). Even after multivariate adjustment, MS was still associated with higher risk of in-hospital heart failure (odds ratio (OR), 1.37; 95% CI: 1.03-1.81; p=0.028) and mortality (OR, 4.42; 95% CI: 1.25-15.5; p=0.020). CONCLUSIONS: Prevalence of MS in ACS patients in Oman is high and seen more in females than in males. Furthermore, MS was associated with higher in-hospital heart failure and mortality.