The standard treatment for patients with locally advanced non-small-cell lung cancer (LA-NSCLC) is chemoradiotherapy (CRT), but surgical resection following induction CRT can extend overall survival in a select population. However, patients who survive longer are at risk of developing a second primary cancer (SPC). This is the first report to determine the incidence of SPC in survivors with LA-NSCLC after trimodal therapy. Between October 1997 and October 2013, 112 Stage III NSCLC patients underwent trimodal therapy in our hospital. The 5-year overall survival rate was 71.8%. SPC developed in 10 of the 112 patients 0.60-15.0 (median 5.49) years after initiating CRT. The observed incidence of SPC was 1.8 per 100 patient-years. Although trimodal therapy can prolong patient survival, the estimated incidence of SPC does not increase. A large prospective study with a longer follow-up time is required to determine the effects of trimodal therapy, including the development of SPC.