BACKGROUND: Acute myeloid leukemia (AML) in monozygotic twins is a rare event and, until now, only a few cases have been reported. Due to improved oncological treatment and cancer survival rates, quality of life considerations post-treatment have become an important aspect in the treatment regime. The ability to have their own biological children is considered one of the most important indicators of quality of life by cancer survivors. As fertility following oncological treatment is often impaired, fertility preservation methods should be offered to these patients prior to the treatment. Here, we present a very rare case in which we can in vivo observe the impact of oncological treatment on female fertility when applied before and after puberty. CASE PRESENTATION: This is a very rare case of concordant AML in monozygotic twin sisters. Twin A became sick at the age of 21 months. She was treated with cytostatic medications and then underwent bone marrow transplantation (BMT), the donor being her twin sister B. After 27 years, she is disease free and has regular periods. After trying to conceive for 4 years, she was seen by an infertility specialist. She underwent hysteroscopic uterine septum removal and laparoscopic enucleation of bilateral paraovarian cysts. Following those procedures, she immediately conceived naturally. Twin B became sick at 15 years of age. She was treated with chemotherapy and cranial radiation and relapsed after 10 years. She then received chemotherapy and had a BMT. Until relapse, she had normal menstrual cycles. After the second treatment she became amenorrhoeic and is now part of an oocyte donation program. CONCLUSIONS: This is a case of AML in monozygotic twins who, after treatment, have completely different reproductive potential. They both received oncological treatment, and one of them conceived conceived naturally while the other suffered premature ovarian failure and is not able to have a biological child. Based on the outcome of this case, it appears that the pre-pubertal state truly serves as protection against ovarian failure.