The 21-gene recurrence score (RS) assay is prognostic in estrogen receptor-positive (HR+), HER2-negative, node-negative breast cancer (BC). The interaction between RS and host factors including metabolic syndrome (MS) is unclear. MS conditions such as obesity have been associated with worse BC prognosis. The aim of this study was to identify associations between presence of MS conditions and RS group or breast cancer recurrence. Demographic, pathologic, and treatment data, MS criteria, and menopausal status were abstracted from medical records of women with stage I–II, HR+, HER2-negative BC evaluated with the RS assay at a single institution since 2005. MS was defined as presence of ≥3 of the following within 2 years of diagnosis: body mass index ≥27.7 kg/m2; hypertension; impaired fasting glucose; HDL <50 mg/dL; hypertriglyceridemia. Of 533 eligible women, 22 % had MS. MS was more common in post- vs premenopausal women (30 vs 9 %; P < 0.0001). There was no significant association between RS group and overall MS status or any individual criterion, controlling for stage, and no association after stratification by menopausal status. Postmenopausal status was associated with higher RS group (P = 0.039), independent of stage. With 4.2-year median follow-up, no association between disease recurrence and MS was identified. Although MS has been associated with worse BC outcomes, we were unable to identify associations between RS group and MS criteria. Identification of prognostic factors other than RS that underlie this higher risk will be important for optimizing breast cancer treatment decision-making in patients with MS.