[Cyst, endometriosis, borderline tumor, CUP : diagnostic stations of a supposedly simple renal cyst].

Symptomatic renal cysts are not uncommon and can be treated by puncture, sclerotherapy, or laparoscopic fenestration. We report the case of a female patient in whom the diagnosis of a supposedly simple symptomatic renal cyst changed over endometriosis and borderline malignancy to a CUP. This case shows that in spite of all diagnostic measures and care the final diagnosis can be a surprise.