Ovarian failure is a major long-term adverse event following gonadotoxic treatment of malignant diseases. Ovarian tissue cryopreservation can be offered in some conditions to preserve fertility. We report the case of a 13-year-old female with a diagnosis of acute myeloid leukemia, who presented with hypergonadotropic hypogonadism after unilateral ovariectomy for fertility preservation and before highly gonadotoxic treatment. Even though damage seemed only partial, this case suggests that the remaining contralateral ovarian function may be compromised after ovarian tissue cryopreservation, leading per se to a hypergonadotropic hypogonadism. Although indication of ovarian cryopreservation is not called into question in situations of highly gonadotoxic therapy, this procedure should only be performed after evaluation by a specialized multidisciplinary team and provided a solid indication.