 The role among metabolic syndrome and breast cancer risk is not well understood and must be further explored. The objective of this study is to evaluate the association between metabolic syndrome and breast cancer in Southern Brazil. In this case-control study, breast cancer patients and controls without malignant disease, matched for age 5 years and menopausal status, were interviewed and asked to make a glucose, HDL-cholesterol and triglycerides test. Waist circumference and blood pressure were measured using standardized procedures. Metabolic Syndrome was considered by NCEP ATP III 2001 and IDF 2006 definitions. Cases and controls were compared in relation to the presence of diagnosed MetS yesno, number of metabolic abnormalities identified 1 to 5 for each definition, and according to each metabolic abnormality cutoff point. 