Sex cord-stromal tumours are a group of tumours derived from the stromal component of the ovary and testis that comprise granulosa, thecal, Sertoli, and Leydig cells as well as fibrocytes. Sertoli-Leydig cell tumours (SLCTs) are rare ovarian neoplasms, accounting for less than 1% of all cancers arising from this organ. They differ in size; some might be very small, while some of them are huge (from < 1 cm to 35 cm). Most SLCTs are unilateral and may be functionally diverse. Approximately one-fifth of SLCTs may contain various heterologous elements, e.g. gastric or intestinal-like epithelium or malignant parts. Women with SLCTs may suffer from hormonal disturbances, manifest high alpha-fetoprotein, CA125, and testosterone levels and may suffer from virilisation, oligomenorrhoea, hirsutism, acne, voice changes, clitoris hypertrophy, or alopecia. However, those symptoms do not occur in every case.

Diagnosis of SLCTs is not easy, due to its rarity and varied presentation. Even though SLCTs are rare tumours, they should always be considered as a possibility, even in patients at different ages (typically 20-30 years old) without raised markers and hormonal disturbances.

In this manuscript we report a case of SLCT, 15 cm in diameter, with low marker levels and lacking hormonal disturbances, found in a 36-year-old female.