Isolated nodal failure (INF) without synchronous local or distant failure is an uncommon occurrence after stereotactic body radiation therapy (SBRT) for lung cancer. Here we review the natural history and patterns of failure after post-SBRT INF with or without salvage mediastinal radiotherapy (SvRT). Patients treated with SBRT for non–small cell lung cancer with definitive intent were identified. Patients who experienced hilar or mediastinal INF without synchronous distant, lobar, or local failure were included and grouped according to the use of SvRT. The rates of subsequent locoregional control, distant metastases, progression-free survival (PFS), and overall survival were assessed. Of 797 patients treated with definitive SBRT, 24 (3%) experienced INF and 15 (63%) received SvRT. The most common SvRT regimen (53%) was 45 Gy in 15 fractions. The median follow-up after INF was 11.3 months for survivors. There were no grade 3 or higher toxicities after SvRT. The 1-year Kaplan-Meier PFS and overall survival estimates were 33% and 56% for patients not receiving radiotherapy and 75% and 73% with SvRT. After SvRT, the rate of locoregional control at 1 year was 84.4%. Crude rates of distant failure were 20.0% with SvRT and 22.2% with no radiotherapy. Of the 13 deaths observed, five (38%) were related to distant progression of lung cancer, four (31%) to comorbidities, three (23%) to mediastinal progression, and one (8%) to an unknown cause. INF is uncommon after SBRT. Despite the significant comorbidities of this population, intrathoracic progression remains a contributor to morbidity and mortality. SVRT for INF is well tolerated and may improve PFS.