SUMMARY Cancer of unknown primary (CUP) syndrome presenting as metastatic lymph nodes of unknown primaries in the head and neck is a difficult clinical problem. The optimal treatment policy is not yet defined. A retrospective analysis of the clinical outcome and side effects of 41 patients with CUP syndrome treated with different irradiation techniques is given in this report. Tweny-eight patients received "involved field" irradiation confined to the involved neck and all the other patients were treated with "extended fields" including the contralateral neck and oro-and hypopharynx. The relative risk of recurrence was 30% and 56% after 1 and 3 years for patients irradiated with "involved fields" and 56% for both periods for patients treated with "extended fields." During follow-up the primary tumor was detected in 11 patients. In conclusion, after thorough diagnostic workup and surgery, limited radiotherapy to the involved neck is justified. Rudiut