Dedifferentiated metastatic melanoma can pose a significant diagnostic challenge, especially if the history of primary melanoma is not known or is remote. BRAF and NRAS mutations are common melanoma driver mutations that are usually sequenced to evaluate for treatment targets. We evaluated whether BRAF and NRAS mutational testing could contribute to the diagnosis of dedifferentiated metastatic melanoma when immunostains are negative. Seven patients with melanoma who had an additional diagnosis of poorly differentiated sarcoma with negative melanocytic immunostains were tested for BRAF and NRAS mutations. Three patients showed identical BRAF mutations in the melanoma and the poorly differentiated sarcoma and hence were re-classified as metastatic dedifferentiated melanoma. In these three patients, there was an average delay of 7 months before appropriate testing, workup and treatment for metastatic melanoma was initiated. Two of these patients currently have stable metastatic disease and show sustained therapeutic response to melanoma-specific treatment including BRAF inhibitors. BRAF mutational analysis should therefore be considered in cases of poorly differentiated sarcoma, especially if there is a known history of melanoma or with unusual localization of disease. The administration of melanoma-specific treatments in such dedifferentiated cases can show therapeutic response, highlighting the importance of rendering accurate diagnoses on such cases.