Rhabdomyosarcoma (RMS) is a highly invasive malignant soft tissue sarcoma that rarely affects adults. The head and neck region accounts for most adult RMSs. Here, we report a case of a 24-year-old Caucasian woman who was diagnosed with persistent hoarseness and a painless left-sided neck mass. Physical examination and image studies showed a massive tumor of the nasopharynx, extending from the left-sided skull base to supraglottic structures. Histopathologic evaluation revealed the diagnosis of a poorly differentiated RMS. Due to the primary tumor size and involvement of crucial structures, extensive surgical excision was not amenable. Thus, the patient was treated with radiotherapy and chemotherapy. Although very rare, nasopharyngeal RMSs should be considered in the differential diagnosis of neck masses in adult patients. This case report illustrates the difficulty in the diagnosis and treatment of rare head and neck malignancies and encourages its reporting.