Background: The choice of surgical breast cancer treatment represents an opportunity for shared decision making (SDM), since both mastectomy and breast conserving surgery are viable options. Yet women vary in their desire for involvement in this decision. Purpose: To evaluate patient and surgeon correlates of a shared decision for surgical breast cancer treatment, and the concordance between patients' desired and actual roles in this decision. Methods: Study subjects were breast cancer patients of Detroit and Los Angeles SEER registries mailed a questionnaire shortly after diagnosis in 2002 (N=1,800, RR: 77%). Data were merged with a survey of all surgeons (N=456, RR: 80%) for a dataset of 1,547 patients of 318 surgeons. SDM was measured using the Control Preferences Scale and categorized into: 1) surgeon-based decision (with/without patient input); 2) shared decision; 3) patient-based decision (with/without surgeon input). The concordance between a woman's self-reported actual and desired decisional involvement was categorized as more, less, or the right amount. SDM and involvement were dependent variables. The first set of independent variables included patient clinical and demographic and surgeon demographic factors. We then included two sets of surgeon “practice style” factors potentially related to SDM: referral propensity and surgeon reports of participating in SDM. Multinomial logistic regression was done, controlling for clustering within surgeons. Results: 37% of women reported the surgery decision was shared, 25% that it was surgeon-based, and 38% that it was patient-based. Two-thirds experienced the right amount of involvement, while 13% had less and 19% had more. Compared to women who reported a shared decision, those with surgeon-based decision were significantly (p<0.05) more likely to have male surgeons, while those who drove the decision themselves were more likely to be nonwhite and have surgeons with lower procedure volume (p<0.05). Women who were less involved in the surgery decision than they wanted had lower educational attainment, while those with more involvement more often had surgeons reporting medium referral propensity (vs. low) and higher tendencies to participate in SDM. Conclusions: Correlates of SDM and the concordance between women's desired and actual level of involvement in surgical decision making differ, with surgeon practice style factors relating to patients' feeling over-involved in this decision. Determining patients' desired role in decision making may be more important than achieving SDM.