A child was referred for evaluation after prenatal diagnosis with macrosomia, clitoromegaly, labial hypertrophy, and a left ovarian cyst. The karyotype was 46,XX. The postnatal pelvic ultrasound was normal. High levels of anti-mullerian hormone and testosterone led to a hCG stimulation test, which was followed by isosexual precocious puberty and the appearance of a bilateral ovarian enlargement with a left tumoral mass. A left ovarian tumorectomy revealed a fibrothecoma. Six weeks later, a tumoral relapse occurred and completion of oophorectomy revealed a juvenile granulosa cell tumor (JGCT). Whereas hormonal levels decreased after surgery, a new rise associated with an enlargement of the right ovary led to the diagnosis of right JGCT. A right oophorectomy was proposed to the parents, who declined further surgery. After 2 months, the hormonal levels normalized. This case illustrates the confusing overlap between developmental and neoplastic biology in neonates.