Background Patient and tumor characteristics often coincide with obesity, potentially affecting treatment decision-making in obese breast cancer patients. Independent of all of these factors, however, it is unclear whether obesity itself impacts the decision to offer patients undergoing mastectomy breast reconstruction, postmastectomy radiation therapy (PMRT), or neoadjuvant chemotherapy. We sought to determine whether implicit bias against obese breast cancer patients undergoing mastectomy plays a role in their treatment. Methods Medical records of breast cancer patients undergoing mastectomy from January 2010 to April 2018 from a single institution were retrospectively reviewed, separated into obese (BMI ≥30) and nonobese (BMI <30) categories, and compared using nonparametric statistical analyses. Results Of 972 patients, 291 (31.2%) were obese. Obese patients were more likely to have node-positive, triple-negative breast cancers ( P = .026) and were also more likely to have other comorbidities such as a history of smoking ( P = .026), hypertension ( P < .001), and diabetes ( P < .001). Receipt of immediate reconstruction and contralateral prophylactic mastectomy did not vary between obese and nonobese patients. While obese patients were more likely to undergo neoadjuvant chemotherapy (26.5% vs. 18.1%, P = .004) and PMRT (33.0% vs. 23.4%, P = .003), this did not remain significant when controlling for comorbidities and clinicopathologic confounders. Conclusion Obese patients present with more aggressive tumors and often have concomitant comorbidities. Independent of these factors, however, differences in the treatment of patients undergoing mastectomy do not seem to be affected by an implicit bias against obese patients.