Concomitant radiochemotherapy (RTCT) is the standard treatment for unresectable stage III non-small cell lung cancer (NSCLC). However, in patients with a peripheral primary tumor, the irradiated volume may include a large portion of normal lung and RT-CT is not possible. This multicenter phase II trial in unresectable stage III NSCLC with peripheral primary tumor evaluated the feasibility of stereotactic body radiation therapy (SBRT) in peripheral tumor after concomitant radio-chemotherapy (RT-CT). Nineteen patients were included and analyzed (median age, 60.9 years; male, 78%; adenocarcinoma, 74%; median size of peripheral primary tumor, 19 mm). At 6 months, the disease control rate was 79% (15/19). SBRT toxicity was generally mild with one (5%) patient having grade 3 lung toxicity. Recruitment for this study was stopped prior to completion, firstly due to the approval of adjuvant durvalumab after RT-CT, which was not anticipated in the design, and secondly due to the small number of stage III NSCLC patients with a peripheral tumor that was accessible to SBRT. Nevertheless, the combination of RT-CT and SBRT appeared to be feasible and safe.