Stereotactic Ablative Radiotherapy (SABR) is a well-established treatment for medically inoperable peripheral stage I non-small cell lung cancer (NSCLC). Previous non-randomised evidence supports SABR as an alternative to surgery, but high quality randomised controlled trial (RCT) evidence is lacking. The SABRTooth study aimed to establish whether a UK phase III RCT was feasible.SABRTooth was a UK multi-centre, randomised controlled feasibility study targeting patients with peripheral stage I NSCLC considered to be at higher-risk of surgical complications. Fifty-four patients were planned to be randomised 1:1 to SABR or surgery. The primary outcome was monthly average recruitment rates.Between July 2015 and January 2017, 318 patients were considered for the study and 205(64.5%) were deemed ineligible. Of 106 assessed as eligible (33.3%), 24 patients (22.6%) were randomised to SABR (n=14) or surgery (n=10). A key theme for non-participation was treatment preference with 43 (41%) preferring non-surgical treatment and 19(18%) preferring surgery. The average monthly recruitment rate was 1.7 patients against a target of 3. Fifteen patients underwent their allocated treatment, 12 SABR, 3 surgery.We conclude that a phase III RCT randomising higher-risk patients between SABR and surgery is not feasible in the National Health Service (NHS). Patients have pre-existing treatment preferences, which was a barrier to recruitment. A significant proportion of patients randomised to the surgical group declined and chose SABR. SABR remains an alternative to surgery and novel study approaches are needed to define which patients benefit from a non-surgical approach.