Systemic therapies have been shown to effectively improve prognosis in patients with breast cancer. However, such therapies also become increasingly harmful as their duration increases, and they have adverse effects on fertility and ovarian function. Fertility preservation (FP) is important in young adult cancer survivors who may wish to have children. In Japan, some cancer societies recommend that the potentially serious effects of systemic therapy on ovarian function should be explained to women with cancer, and they should be encouraged to undergo FP prior to commencing treatment. Still, as there are no official guidelines, many oncologists lack the required knowledge and mind-set to advise young breast cancer patients on fertility issues. Counseling of patients and their families might improve their understanding about the influence of such treatment on fertility and ensure effective FP. There are several FP methods that can be selected before beginning treatment, and these methods have both advantages and disadvantages. Young adults with breast cancer who want to bear children in the future must be provided with FP counseling, in addition to advice about breast cancer treatment and prognosis.