Introduction. Adenomyosis is a widespread disease usually affecting the late reproductive years of the women’s life, which has a great impact on their fertility. The most common form is diffuse adenomyosis, while focal adenomyosis, a cystic variant, is very rare, particularly in patients younger than 30 years old.

Materials and methods. We reported a rare case of a 20-year-old Caucasian woman with cystic adenomyosis who was admitted in our service with severe chronic pelvic pain, dysmenorrhea, and menorrhagia, who had received conservative surgical treatment to preserve fertility and improve her obstetrical prognosis.

Results and Discussions. Although the necrobiosis of a uterine fibroid was suspected preoperatively, the extemporaneous histopathological exam revealed adenomyosis associated with fibroleiomyoma with hyaline dystrophy and multiple foci of endometriosis of cystic formation in the wall of a young woman without any risk factors.

Conclusion. Although a rare lesion in young patients, cystic adenomyosis should be considered when chronic pelvic pain is exacerbated during menstruation and is associated with a uterine tumor. In young patients, the differential diagnosis should be made with uterine malformations (hematometra), necrobiosis of uterine fibroids, pelvic endometriosis. The surgical treatment should be conservative with the excision of the lesion, always taking into account fertility preservation in young patients.