Background <p>Lung and bronchial cancer is the most diagnosed cancer among both sexes in Canada and has one of the lowest survival rates.</p> Methods <p>This population level retrospective cohort study examined the associations between the lung cancer stage at diagnosis and English/French fluency. The study used multiple linked health-administrative databases to create a cohort of urban-dwelling Ontarian immigrants and long-term residents aged 45–105 diagnosed with incident lung cancer between 1 January 2010 and 31 December 2020. Modified Poisson regression was used to examine the risk of diagnosis at early vs. late stages among immigrants who do not speak English or French fluently compared with immigrants who speak English or French fluently. The fully adjusted model included age, sex, neighborhood-area income quintile, lung cancer type, number of primary care visits prior to diagnosis, and region of origin.</p> Results <p>Approximately 57.7% of the 96,613 people diagnosed with incident lung cancer between 2010 and 2020 were diagnosed at the late stage. Non-English/French fluent immigrants were no more likely to be diagnosed at a late stage than English/French fluent immigrants and long-term residents (57.6% vs. 57.8% and 57.7%). However, in fully adjusted models, people living in lower neighborhood income quintiles were more likely to be diagnosed at a late stage (e.g., income quintile 1 [lowest] vs. quintile 5 [highest]: [ARR 1.08; 95% CI: 1.02–1.15]), as were immigrants from the Caribbean [ARR 1.16; 95% CI: 1.05–1.29] and South Asia [ARR 1.10; 95% CI: 1.02–1.19].</p> Conclusions <p>Although lung cancer is frequently diagnosed at a late stage in Ontario and we found socioeconomic inequalities, fluency in Canada’s official languages was not associated with late diagnosis in this study.</p>