•TORS work-up of the unknown primary led to a reduction in treatment volume and dosing of radiotherapy.•Resection of the primary tumor by TORS was associated with avoidance of chemotherapy. Our primary objective is to describe the post- operative management in patients with an unknown primary squamous cell carcinoma of the head and neck (HNSCC) treated with trans-oral robotic surgery (TORS). We conducted a retrospective multi-institutional case series including all patients diagnosed with an unknown primary HNSCC who underwent TORS to identify the primary site from January 1, 2010 to June 30, 2016. We excluded those with recurrent disease, ≤6months of follow up from TORS, previous history of radiation therapy (RT) to the head and neck, or evidence of primary tumor site based on previous biopsies. Our main outcome measure was receipt of post-operative therapy. The tumor was identified in 26/35 (74.3%) subjects. Post-TORS, 2 subjects did not receive adjuvant therapy due to favorable pathology. Volume reduction of RT mucosal site coverage was achieved in 12/26 (46.1%) subjects who had lateralizing tumors, ie. those confined to the palatine tonsil or glossotonsillar sulcus. In addition, for 8/26 (30.1%), the contralateral neck RT was also avoided. In 9 subjects, no primary was identified (pT0); four of these received RT to the involved ipsilateral neck nodal basin only without pharyngeal mucosal irradiation. Surgical management of an unknown primary with TORS can lead to deintensification of adjuvant therapy including avoidance of chemotherapy and reduction in RT doses and volume. There was no increase in short term treatment failures. Treatment after TORS can vary significantly, thus we advocate adherence to NCCN guideline therapy post-TORS to avoid treatment-associated variability.