Sex cord–gonadal stromal tumour is a group of tumors derived from the stromal component of the ovary and testis, which comprises the granulosa, thecal cells and fibrocytes. In contrast, the epithelial cells originate from the outer epithelial lining surrounding the gonad while the germ cell tumors arise from the precursor cells of the gametes, hence the name germ cell. In humans, this group accounts for 8% of ovarian cancers and under 5% of testicular cancers. Their diagnosis is histological: only a biopsy of the tumour can make an exact diagnosis. They are often suspected of being malignant prior to operation, being solid ovarian tumours that tend to occur most commonly in post menopausal women. This group of tumours is significantly less common than testicular germ cell tumours in men, and slightly less common than ovarian germ cell tumours in women (see Ovarian cancer). Types Tumour types in order of prevalence Granulosa cell tumour. This tumour produces granulosa cells, which normally are found in the ovary. It is malignant in 20% of women diagnosed with it. It tends to present in women in the 50-55yo age group with post menopausal vaginal bleeding. Uncommonly, a similar but possibly distinct tumour, juvenile granulosa cell tumour, presents in pre-pubertal girls with precocious puberty. In both groups, the vaginal bleeding is due to oestrogen secreted by the tumour. In older women, treatment is total abdominal hysterectomy and removal of both ovaries. In young girls, fertility sparing treatment is the mainstay for non-metastatic disease. Sertoli cell tumour. This tumour produces Sertoli cells, which normally are found in the testicle. This tumour occurs in both men and women. Thecoma. This tumour produces theca of follicle, a tissue normally found in the ovarian follicle. The tumour is almost exclusively benign and unilateral. It typically secretes estrogen, and as a result women with this tumour often present with postmenopausal bleeding. Leydig cell tumour. This tumour produces Leydig cells, which normally are found in the testicle and tend to secrete androgens. Sertoli–Leydig cell tumour. This tumour produces both Sertoli and Leydig cells. Although both cell types normally occur in the testicle, this tumour can occur in the ovary. Gynandroblastoma. A very rare tumour producing both ovarian (granulosa and/or theca) and testicular (Sertoli and/or Leydig) cells or tissues. Typically it consists of adult-type granulosa cells and Sertoli cells, but it has been reported with juvenile-type granulosa cells. It has been reported