This review examines evidence that weight gain in the years leading up to the menopause can contribute to a woman's risk of postmenopausal breast cancer and may involve perimenopausal stimulation of growth in cancer precursor lesions. We used the Medline database since 1980 to examine studies that assessed the association between increased risk of postmenopausal breast cancer and perimenopausal weight gain or abdominal fat accumulation. This review examines possible mechanisms by which the endocrine-metabolic concomitants of hyperinsulinemia may act as late-stage promoters of mammary carcinogenesis. It was found that, in obese postmenopausal women with breast cancer, excess weight is likely to have been gained before menopause. In Western women, evidence of abdominal obesity associated with hyperinsulinemia increases progressively after the age of 40. Weight gain in the years leading up to the menopause mainly involves abdominal obesity which is associated with insulin resistance, increased free estrogen levels, and imbalance in sex steroids levels. These endocrine-metabolic changes are likely to inhibit the tendency for cancer precursor lesions to regress at the menopause and may lead to late-stage promotion of mammary carcinogenesis.