Fertility is important to young breast cancer survivors (YBCS). Treatment for breast cancer increases the risk of infertility. Fertility preservation prior to breast cancer treatment aims to improve options for fertility post-treatment. Fertility preservation decisions are challenging for YBCS. In retrospective cohort studies, YBCS that underwent fertility preservation experienced less decisional regret after primary cancer treatment. Objectives and hypotheses: to assess longitudinal changes in decisional regret on fertility preservation following breast cancer diagnosis; to determine if fertility concerns and fertility preservation treatment decisions are related to decisional regret.