"Translation" of the current "basic science" information related to physical activity into patient intervention programs is needed. This translation is critical to providing benefit to the maximum number of patients. Little is known about the determinants of physical activity among breast cancer patients undergoing hormonal therapy and few studies have attempted to evaluate an exercise behavior change program aimed to improve exercise adherence among such patients. The proposed project will evaluate use of an innovative behavioral and psychosocial intervention to increase physical activity among breast cancer patients.

Inclusion Criteria:

• Female breast cancer patients between the ages of 18 and 70 years of age with a diagnosis of Stage I, II, or IIIA breast cancer who are currently taking aromatase inhibitors or selective estrogen receptor modulators for the next 8 months.
• English speaking
• Medical clearance for participation provided by primary care physicians
• If the patient has undergone a surgical procedure, must be at least 6 weeks post-procedure

Exclusion Criteria:

• Diagnosis of dementia or organic brain syndrome
• Medical, psychological or social characteristic that would interfere with ability to fully participate in program activities and assessments (e.g., psychosis, schizophrenia, etc.)
• Contraindication to participation in a regular physical activity program.
• Metastatic or recurrent disease
• Inability to ambulate
• Engaged in >/= 60 minutes of vigorous physical activity or >/= 150 minutes of moderate plus vigorous physical activity per week during the past month.