There is growing evidence that obesity is associated with poor outcomes in early stage breast cancer. This paper addresses four current areas of focus: 1. Is obesity associated with poor outcomes in all biologic subtypes of breast cancer? 2. Does obesity effect AI efficacy or estrogen suppression in the adjuvant setting? 3. What are the potential biologic underpinnings of the obesity-breast cancer association? 4. Are intervention studies warranted? If so, which interventions in which populations? Research is needed to resolve these questions; intervention trials involving lifestyle interventions or targeting the biology postulated to link obesity and cancer are recommended.