['Patients with stage I non-small-cell lung cancer (NSCLC) treated with stereotactic body radiotherapy (SBRT) do not undergo a staging mediastinoscopy, yet reported mediastinal recurrence rates appear lower than in patients undergoing surgical resection. We determined incidental SBRT doses to assess whether this could account for the low rates of recurrence.', 'Between March 2009 and September 2012, we reviewed cases of patients with inoperable lung tumors (n = 136) treated with SBRT at our institution. The SBRT regimen was 54 Gy in 3 fractions with positron emission tomography/computed tomography (PET/CT) staging. Incidental doses to the mediastinal lymph node stations (MLNSs), primary tumor control, locoregional (LR), distant control (DC), and overall survival (OS) rates were determined.', 'Forty-six patients with stage I NSCLC met the inclusion criteria. The calculated median incidental SBRT dose to all MLNSs was < 5 Gy for the majority of patients (75%). At a median follow-up of 16.8 months (0.6-38.9 months), the 1- and 2-year primary tumor control, LR, OS, and DC rates were 100% and 95.5%, 97.4% and 81.7%, 88.1% and 81%, and 96.9% and 86.9%, respectively. Only 2 patients (4.9%) had mediastinal recurrence, with incidental SBRT doses to MLNSs that were similar to the rest of patients (P > .05).'] Does incidental mediastinal dose explain low mediastinal node recurrence rates in patients with early-stage NSCLC treated with stereotactic body radiotherapy?