Weight gain is a common and persistent problem for many breast cancer survivors and is associated with adverse health consequences. A comprehensive review of the English language literature was conducted to investigate the frequency, magnitude and pattern of weight gain among breast cancer survivors, to identify factors that are associated with these changes and to review the clinical significance of weight gain on disease free survival and overall health. While there appears to be a general trend toward a reduction in the magnitude of weight gain in recent years, as many as 50–96% of women experience weight gain during treatment and many, including some women who remain weight stable during treatment, report progressive weight gain in the months and years after diagnosis. Weight gain is more common in women receiving adjuvant chemotherapy, especially for women receiving longer duration treatments and seems to be especially pronounced in premenopausal women. With or without weight gain, unfavourable changes in body composition including fat gain and loss of lean tissue are prevalent. This unique pattern of weight gain and change in body composition is distressing for most women, poses significant risk for the development of co-morbid conditions and may impact on long term disease-free survival.