Introduction: Primary dermal melanoma (PDM) is a recently described clinical entity accounting for less than 1% of all melanomas. Histologically, it is located in the dermis or subcutaneous tissue, and it shows no connections with the overlying epidermis. The differential diagnosis is principally made along with that of metastatic cutaneous melanoma. Case Report: A 72-year-old Caucasian woman with a history of multiple cancers (metachronous bilateral breast cancer, meningioma, clear cell renal cell carcinoma, uterine fibromatosis and intestinal adenomatous polyposis), came to our attention with a nodular lesion on her back. After removal of the lesion, the histology report indicated malignant PDM or metastatic malignant melanoma. The clinical and instrumental evaluation of the patient did not reveal any other primary tumour, suggesting the primitive nature of the lesion. The absence of an epithelial component argued for a histological diagnosis of PDM. Subsequently, the patient underwent a wide surgical excision with sentinel node biopsy, which was positive for metastatic melanoma. Finally, the mutational status was studied in the main genes that regulate proliferation, apoptosis and cellular senescence. No pathogenetic mutations in CDKN2A, BRAF, NRAS, KRAS, cKIT, TP53 and PTEN genes were observed. This suggests that alternative pathways and low-frequency alterations may be involved. Conclusions: The differential diagnosis between PDM and isolated metastatic melanoma depends on the negativity of imaging studies and clinical findings for other primary lesions. This distinction is important because 5-year survival rates in such cases are higher than in metastatic cases (80-100 vs. 5-20%, respectively).