Background: For patients with unresectable, previously radiated, locoregionally recurrent head and neck cancer, stereotactic body radiation therapy (SBRT) has become an attractive option. The use of high daily doses of radiotherapy may overcome the inherent radioresistance of these recurrent cancers. Given the resistant and advanced nature of many of these cancers, the addition of chemotherapy to radiotherapy is typically recommended as a radiosensitizer. We therefore performed a phase I clinical trial in order to establish a maximum tolerated dose of SBRT with concurrent chemotherapy in locoregionally recurrent head and neck cancer. Methods: Major inclusion criteria were recurrence of previous squamous cell carcinoma of the head and neck in patients who had previously undergone radiotherapy to doses ≥ 45 Gy to the area of recurrence, ≥ 6 months prior to enrollment, and who were medically unfit for surgery, deemed unresectable, or refused surgery. Patients were treated with radiation therapy every other day for five fractions at three dose levels; 30 Gy, 35 Gy, and 40 Gy. Cisplatin was given prior to every SBRT fraction at a dose of 15 mg/m2. Patients were monitored for safety and tolerability for any grade 4 or greater toxicity (per CTCAE v4.0) that occurred within 3 months from the start of SBRT. Primary end point was maximum tolerated dose (MTD). Results: Twenty patients were enrolled and of those 17 patients were evaluable for the primary endpoint. Nine patients had a primary tumor in the oropharynx, four patients in the oral cavity, three in the neck, one in the larynx, and one simultaneously in the larynx and neck. Of the three patients that were not evaluable two withdrew consent, and one patient in the 30 Gy dose level died of unknown causes two weeks following completion of treatment. Due to safety concerns the 30 Gy dose level was expanded an additional three patients, and no further dose limiting toxicities (DLTs) were observed. At the 35 Gy and 40 Gy dose level there were no reported grade 4 or 5 adverse events (per CTCAE v4.0). There were 5 (27%) reported grade 3 toxicities and 12 (66%) grade 2 toxicities. Conclusions: This phase I study demonstrates that 40 Gy SBRT with concurrent cisplatin at a dose of 15mg/m2 is feasible, safe, and well tolerated. Patients continue to be followed for secondary outcomes of local control and overall survival. Clinical trial information: NCT02158234.