In Chile breast cancer (BC) is the first cause of death in women. While the most important risk factor for its development is estrogenic stimulation, environmental factors and lifestyles also contribute to its pathogenesis. Epidemiological studies show a direct relationship between physical activity (PA), incidence and recurrence of BC. Supervised PA practice is recommended in most cancer patients to improve their quality of life, to reduce adverse effects from treatment and eventually to improve the prognosis of the disease. We review the epidemiological evidence linking PA and BC and the biological basis of this relationship. We also review the relevant interventional studies and we explore some practical indications of PA in patients with BC, as a model for other tumors of epidemiological importance.