To date, only a limited number of studies have examined the impact of ambient pollutant policy on respiratory morbidities. This accountability study examined the effect of a regional pollution control policy, namely, the US Environmental Protection Agency's (EPA) nitrogen oxides (NO(x)) Budget Trading Program (NBP), on respiratory health in New York State (NYS). Time-series analysis using generalized additive models was applied to assess changes in daily hospitalizations for respiratory diseases in NYS after the implementation of the NBP policy. Respiratory end points in the summers during the baseline period (1997-2000) were compared with those during the post-intervention period (2004-2006). Stratified analyses were also conducted to examine whether health impacts of the NBP differed by socio-demographic, regional, or clinical characteristics. Following the implementation of EPA's NBP policy, there were significant reductions in mean ozone levels (-2% to -9%) throughout NYS. After adjusting for time-varying variables, PM(2.5) concentration, and meteorological factors, significant post-intervention declines in respiratory admissions were observed in the Central (-10.18, 95% confidence interval (CI): -14.18, -6.01), Lower Hudson (-11.05, 95% CI: -16.54, -5.19), and New York City Metro regions (-5.71, 95% CI: -7.39, -4.00), consistent with wind trajectory patterns. Stratified analyses suggest that admissions for asthma, chronic airway obstruction, among those 5-17 years old, self-payers, Medicaid-covered, and rural residents declined the most post-NBP. This study suggests that the NO(x) control policy may have had a positive impact on both air pollution levels statewide and respiratory health in some NYS regions. However, the effect varied by disease subgroups, region, and socio-demographic characteristics.