Background: Disparities in clinical trial participation can mean disparities in medical advances, and disproportionate participation is an ethical issue even if differential results are not expected. The disparate impact of Covid-19 highlighted the importance of representativeness in trials aiming to prevent or treat disease. Previous analyses suggest there are likely significant differences in cancer clinical trial participants by race, ethnicity, and age. However, these analyses generally compare trial demographics to broad population demographics. Methods: This analysis used the SEER-Medicare linked database with claims data from 2014-2016 to compare lung cancer clinical trial participants to similar lung cancer patients not participating in a treatment trial. We compared the race, ethnicity, sex, age, and number of comorbidities for Medicare beneficiaries with at least one claim for an active treatment for lung cancer to the demographics of Medicare beneficiaries with at least one claim coded with the National Clinical Trials (NCT) number for an active treatment trial in lung cancer. The relationship between clinical trial participation and demographic variables was assessed using chi-square tests for binary variables and t-tests for continuous variables and corrected for multiplicity. A logistic regression model was used to assess robustness of these findings. Clinical trial participants were hypothesized to be more likely to be White, non-Hispanic, and male, and have a lower mean age and fewer comorbidities than the comparable non-trial active treatment population. Results: We compared 1,624 lung cancer clinical trial patients to 34,077 active treatment lung cancer patients. Clinical trial participants were more likely than non-trial active treatment patients to be female (53.6% vs. 50.4%, p = 0.015) or Asian/Pacific Islander (13.0% vs. 5.2%, p < 0.001) and less likely to be Black (5.2% vs. 9.0%, p < 0.001) or White (76.5% vs. 81.4%, p < 0.001). Trial participants had a lower mean age (70.7 vs. 73.7, p < 0.001) and fewer comorbidities (3.0 vs. 4.6, p < 0.001). There was not a significant difference by Hispanic ethnicity (5.2% vs. 4.4%, p = 0.106). The regression analyses supported these findings. Conclusions: Most analyses of clinical trials enrollment do not have a direct comparison group. Because this study is directly comparing lung cancer trial participants and non-participants from the same Medicare beneficiary population, the results fill a gap in our understanding of disparities in cancer clinical trial participation. Trial participants in this analysis were more representative than hypothesized, although the results supported previous findings that Black patients and older patients are underrepresented in cancer trials. There was also lower participation by White patients. Underrepresentation of patients with comorbidities may be due to trial eligibility criteria.