We present a case of Sertoli-Leydig cell tumour of the ovary in a 14-year-old girl who presented with abdominal distension. Ultrasonography showed a multilocular cystic lesion filled with finely echogenic fluid. Contrast-enhanced CT demonstrated a huge multilocular cystic mass with thickened septa. At MR imaging, the capsule of the cyst was focally thickened, showing intermediate signal intensity on T2-W images. Although extensive cyst formation of Sertoli-Leydig cell tumour is rare, this tumour should be considered in the differential diagnosis of a multilocular cystic ovarian tumour in a young female.