Background: Concurrent chemoradiation therapy (cCRT) in patients with unresectable stage III non-small cell lung cancer (NSCLC) is an NCCN guideline recommendation. However, little is known about the proportions of patients in this population that receive chemoradiation therapy (CRT), concurrent or sequential (sCRT). Objective: To estimate the proportions and characteristics (age, gender, comorbidities) of unresectable Stage III NSCLC patients receiving cCRT and sCRT. Methods: Diagnosis, procedure, and drug codes were used to select patients ≥18 years of age with an index lung cancer diagnosis from 1 July 2013 to 30 September 2017 with follow-up through March 2018 from the IBM MarketScan Commercial (COM) and Medicare (MED) databases. Included patients had continuous health plan enrollment during a 6-month pre- and post-index period and a claim for chemotherapy or radiation during the post-index period. Excluded patients had evidence of antineoplastic drugs (pre-index period), other primary cancers (pre- and post-index periods), lung resection, SCLC treatments (drugs or prophylactic cranial irradiation), lung metastases, or palliative care only (≤10 radiotherapy claims with no chemotherapy during the post-index period). Patients with a radiation claim nested between two chemotherapy claims, or a chemotherapy claim nested between two radiation claims were deemed to have received cCRT. Patients with sCRT had chemotherapy and radiation within 180 days following their index dates, with the first two treatments occurring within 60 days of each other. Proportions equaled the number of patients receiving CRT divided by the number with a claim for an oncologist, radiologist, or nuclear medicine specialist visit with subsequent claim(s) for chemotherapy or radiation, excluding palliative care patients. Results: 1,296 (COM) and 1,796 (MED) patients remained after imposing the selection criteria. Among these, 55.1% (COM) and 49.3% (MED) received cCRT and 6.3% received sCRT (COM, MED). All COM and <5% MED patients were ≤65 years of age. Within CRT cohorts, males had relatively more cCRT use (cCRT: 56.4% (COM) and 57.3% (MED) vs sCRT: 48.1% (COM) and 53.8% (MED). COPD, dyslipidemia, and hypertension were the most common comorbidities across cohorts (Table 1). Conclusions: Approximately 50% of unresectable Stage III NSCLC patients received the treatment recommended in the NCCN guidelines (COM and MED). Comorbidity and gender percentages varied across CRT cohorts.