Purpose Lung cancer incidences tend to be higher among males than females in both China and the United States, yet secular incidence patterns are different due to distinct population and environmental exposures. We examined long-term and future trends of lung cancer incidence, as well as the associations of age, period, and cohort effects with gender disparities. Methods Using data from the Cancer Incidence in Five Continents from 1978 to 2012, we calculated age-standardized, age-specific incidence, and male-to-female incidence rate ratios (IRR), and conducted an age-period-cohort analysis. The average annual percentage change (AAPC) of the trends was obtained by Joinpoint Regression. Bayesian age-period-cohort analysis was also conducted to project incidences to 2032. Results In China, age-standardized incidence revealed a decreasing trend among males, but showed increasing trends among the younger age groups (30-54 years) in females. Age-standardized incidence rates of males decreased but remained stable among females from 1972 to 2012 in the United States. Male-to-female incidence rate ratios narrowed in both countries and reversed among younger birth cohorts in the United States. Gender disparities are expected to continue to diminish in both countries, and incidence among females appears to exceed that of males in the United States by around 2023-2027. Conclusion Gender disparities in lung cancer incidence persist and will continue into the future in both countries, but our findings suggested that smoking may play different roles in gender disparities in lung cancer incidence between the two countries. Further population-based epidemiological studies among females in China are imperative.