Background: In elderly patients with lung cancer, race/ethnicity is associated with not receiving treatment; however, little attention has been given to nonelderly patients (aged ≤65 years) with a range of disease stages and histologies. Nonelderly patients with lung cancer have superior survival at NCI-designated Comprehensive Cancer Centers (CCCs), although the reasons remain unknown. Patients and Methods: A retrospective cohort study was conducted in 9,877 patients newly diagnosed with small cell or non–small cell lung cancer (all stages) between ages 22 and 65 years and reported to the Los Angeles County Cancer Surveillance Program registry between 1998 and 2008. Multivariable logistic regression examined factors associated with nontreatment. Results: In multivariable analysis, race/ethnicity was associated with not receiving cancer treatment (black: odds ratio [OR], 1.22; P=.004; Hispanic: OR, 1.17; P=.04), adjusting for patient age, sex, disease stage, histology, diagnosis year, distance to treatment facility, type of facility (CCC vs non-CCC), and insurance status. With inclusion of socioeconomic status (SES) in the model, the effect of race/ethnicity was no longer significant (black: OR, 1.02; P=.80; Hispanic: OR, 1.00; P=1.00). Factors independently associated with nontreatment included low SES (OR range, 1.37–2.15; P<.001), lack of private insurance (public: OR, 1.71; P<.001; uninsured: OR, 1.30; P<.001), and treatment facility (non-CCC: OR, 3.22; P<.001). Conclusions: In nonelderly patients with lung cancer, SES was associated with nontreatment, mitigating the effect of race/ethnicity. Patients were also at higher odds of nontreatment if they did not have private insurance or received cancer care at a non-CCC facility. These findings highlight the importance of understanding how both patient-level factors (eg, SES, insurance status) and facility-level factors (eg, treatment facility) serve as barriers to treatment of nonelderly patients with lung cancer.