Introduction Physical inactivity is associated with a higher risk of chronic diseases. Regular stair use can contribute to increasing physical activity in the population. This study aimed to investigate the association between flights of stairs used daily at home and all-cause mortality and cause-specific incidence and mortality. Methods Of the 502,628 UK Biobank participants recruited between 2007 and 2010, 442,027 (mean age, 56±8 years) had available data and were included in the analyses conducted in 2023. Participants were categorized on the basis of flights of stairs climbed daily (1–5, 6–10, 11–15, >15). The disease-specific outcomes were cardiovascular disease, respiratory disease, cancer, type 2 diabetes, and all-cause dementia. Cox proportional hazard models, adjusted for sociodemographic, lifestyle, and health-related confounding factors, were used to analyze the associations between stair use frequency and health outcomes. Results Participants were followed up for a median of 10.9 years. Climbing stairs >15 times per day was associated with a lower risk of 8 of the 9 outcomes analyzed than not using stairs. The magnitude of association ranged from 3% (95% CI=0.94, 0.99) lower risk for all-cause cancer to 51% (95% CI=0.39, 0.60) lower risk of chronic obstructive pulmonary disease. Findings were similar for mortality outcomes, with the hazard ratios ranging from 0.82 (95% CI=0.77, 0.87) for all-cause cancer to 0.46 (95% CI=0.23, 0.92) for chronic obstructive pulmonary disease mortality. Conclusions Stair use was associated with a lower risk of all-cause mortality and cause-specific incidence and mortality independent of confounding factors, including adiposity and multimorbidity.