BACKGROUND: Merkel cell carcinoma (MCC) is a neuroendocrine malignant neoplasm that usually has its primary location on the skin. It often metastasizes to lymph nodes, liver, lungs, bones and brain. Actually there have been few cases of MCC of the retroperitoneal region without a primary skin lesion. CASE PRESENTATION: Our case is a male of 55 year old who initially underwent a partial resection (R1) of a bulky pelvic mass; the histopathological analysis and the immunoistochemistry showed the presence of neuroendocrine Merkel cells. The patient underwent 6 cycles of postoperative chemotherapy (carbon platinum and etoposide) and adjuvant radiotherapy. Afterwards the patient underwent surgery again with the complete resection of the tumour. DISCUSSION: The histopatological and immunoistochemistry analysis of the first and the second surgical samples confirmed the diagnosis of a retroperitoneal high-grade neuroendocrine carcinoma with a high mitosis index. The immunoistochemistry profile showed neoplastic cell with: CD 20+, synaptophysin +, TTF-1-, neurofilaments +, CK 7-, chromogranin, Ki67 90%. In the patient’s medical history no skin localizations were mentioned. CONCLUSION: The hypothesis of a MCC with a primary retroperitoneal localization has been strength by the histopathological and immunoistochemistry analysis of two intra-operative samples from two different surgical procedure and from the absence of either a primary skin location or of secondary recurrences. Is therefore reinforced the theory that from a cell into a retroperitoneal lymph node can arise a retroperitoneal mass originating a Merkel cell tumour.