Evidence is accumulating for physical activity as an effective, well-tolerated, highly rewarding complementary behavioral intervention for enhancing quality of life (QOL) as well as fitness among individuals with chronic and even terminal illnesses. However, relatively few studies have examined the feasibility and potential health benefits of supervised, structured exercise programs for sedentary women with primary breast cancer. Forty women over the age of 45 with primary breast cancer participated in a course of group exercise training (GET) delivered in a structured format three times per week for 16 weeks. GET emphasizes physical activities that promote aerobic fitness, strength, and flexibility. Assessments of fitness/vigor and QOL were conducted prior to, during, and upon completion of the program. Results demonstrated that GET was feasible, safe, and well-tolerated. Moreover, the participants experienced significant health benefits over the course of the intervention in multiple dimensions of fitness/vigor (aerobic capacity, strength, flexibility) as well as QOL (increased positive affect, decreased distress, enhanced well-being, and improved functioning). Discussion highlights the need for inclusion of physical activity programs in comprehensive, complementary treatment regimes for breast cancer patients.