Abstract Disclosure: A. Pataco: None. C.S. Moniz: None. C. Chaves: None. R. Medeiros: None. M. Ponte: None. B.D. Pereira: None. J. Anselmo: None. I. Sousa: None. Premature ovarian failure (POF) is a heterogeneous condition characterized by the cessation of ovarian function leading to amenorrhea before age 40. While the etiology of POF is diverse, the majority of cases are idiopathic, with a likely genetic basis. Xq abnormalities are commonly linked to POF, whereas Xp abnormalities are rare and infrequently reported.We describe a case of a 30-year-old woman with a personal history of depression, presenting to the Endocrinology department with an 8-month history of amenorrhea. Notably, her menstrual cycles had been irregular since menarche. Previously, a gynecological assessment led to the initiation of bromocriptine 5 mg/day for suspected microprolactinoma, indicated by symptoms of galactorrhea, elevated prolactin levels (112 ng/mL; Normal: 5.18-26.53), and a pituitary MRI showing a 3.5mm microadenoma. It is important to note her concurrent use of risperidone, sertraline, and lorazepam at that time.In the first evaluation at the Endocrinology department, the patient reported amenorrhea and denied galactorrhea. The physical examination was unremarkable with no evidence of hirsutism. The blood tests indicated hypergonadotropic hypogonadism, low levels of prolactin and Anti-Müllerian hormone: FSH 17 mIU/mL (Normal: 3.03-8.08), LH 8.30 mIU/mL (Normal: 1.80-11.78), 17-Beta Estradiol 11 pg/mL (Normal: 21-251), Total testosterone 20.1 ng/dL (Normal: 7.21-79.31), TSH 1.84 uIU/mL (Normal: 0.35-4.94), T4L 1.06 ng/dL (Normal: 0.70-1.48), PRL 1.8 ng/mL (Normal: 5.18-26.53), ACTH 21 pg/mL (Normal: 7.2-63.3), Cortisol 11.5 ug/dL (Normal: 3.7-19.4), IGF-1 130.2 ng/mL (Normal: 177-382), Anti-Müllerian hormone <0.1 ng/mL (Normal: 0.3-11.2).A diagnosis of premature ovarian failure was established. Bromocriptine was discontinued, and the hyperprolactinemia was attributed to the iatrogenic effects of her medications. A pelvic ultrasound showed no abnormalities. Cytogenetic analysis revealed an abnormal karyotype: 46 chromosomes with one X chromosome showing an anomalous configuration—partial deletion of the long arm and partial duplication of the short arm [duplication X(p22.33p11.23) with over 100 genes and deletion X(q24q28) including the FMR1 gene].The patient started hormone replacement therapy with estradiol valerate and medroxyprogesterone acetate, achieving regular menstruation thereafter. Literature review reveals that POF cases involving both partial Xp duplication and partial Xq deletion are exceedingly rare (only 6 reported cases). Genetic counseling is recommended for these patients, particularly for those considering parenthood. It is also advisable to assess the chromosomal alteration in parents to determine if the change is inherited and to evaluate the risk to other family members. Presentation: 6/2/2024