Research has been directed towards investigating the role of the trace element, iodine, in breast cancer etiology, diagnosis, and therapy. In many controled studies, iodine has been established as a requirement for breast tissue normalcy, since deficiency of the element results in histopathology consistent with dysplasia and atypia in rodents. Clinically severe hyperplasia and fibrocystic disease is seen in the breasts of women who have low iodine levels. These precancerous lesions result in a high-risk state as well as persistent symptomatology in women. Iodine replacement therapy has been shown to be efficacious in reducing these conditions in clinical trials. Basic research is directed towards intracellular pathways and metabolism for breast iodide, emulating those seen in the thyroid gland. Thus, using a rat model, iodine intracellular organification is being correlated with risk factors for breast cancer including early and late pregnancies, onset of puberty, menopause, and aging. From our research there is significant evidence that iodine maintains homeostasis in reproductive, effected tissues and is responsible for breast tissue growth and development.