Purpose: To analyze the outcome of radiation therapy for patients with a metastatic carcinoma of cervical lymph nodes from an unknown primary (MUO), and identify the prognostic factors for these patients. Materials and Methods: Between July 1981 and June 1999, 39 patients with MUO underwent radiation therapy with curative intent. Twelve patients were treated with radiation therapy alone (Group 1), 8 with neoadjuvant chemotherapy followed by radiation therapy (Group 2), and 19 with either an excision or neck dissection and postoperative radiation therapy (Group 3). There were 31 males and 8 females, with a median age of 55 years, ranging from 25 to 77 ears. The median duration of follow-up was 38 months, ranging from 3 to 249 months. Results: The 5-year overall survival rate was $55\%$. According to the treatment modality, the 5-year disease-free survival rates of Groups 1, 2 and 3 were 48, 19 and $75\%$, respectively (p=0.0324). In addition to the treatment modality, the appearance of the primary site was a significant prognostic factor for disease-free survival (p=0.0085). Conclusion: Surgical resection and radiation therapy achieves a superior disease-free survival compared to radiation therapy alone, either with or without chemotherapy Further investigation Is needed to evaluate the role of chemotherapy in the treatment of MUO.