OBJECTIVE To investigate associations between long-term exposure to PM2.5, NO2, mortality and morbidity in New Zealand, a country with low levels of exposure. METHODS Retrospective cohort study. METHODS The New Zealand resident population. METHODS The main analyses included all adults aged 30 years and over with complete data on covariates: N = 2,223,507. People who died, or were admitted to hospital, (2013-2016) were linked anonymously to the 2013 census, and to estimates of ambient PM2.5, and NO2 concentration. We fitted Poisson regression models of mortality and morbidity in adults (≥30) for all natural causes of death, and by sub- group of major cause. Person-time of exposure, censored at the time of death, was included as an offset. We adjusted for confounding by age, sex, ethnicity, income, education, smoking status and ambient temperature. Further analyses stratified by ethnic group, and investigated respiratory hospital admissions in children. RESULTS There were statistically significant positive associations between pollutants and natural causes of death: RR (per 10 μg/m3) for PM2.5 1.11 (1.07 to 1.15) and for NO2 1.10 (1.07 to 1.12). For morbidity, the strongest associations were for PM2.5 and ischaemic heart disease in adults, RR: 1.29 (1.23 to 1.35) and for NO2 and asthma in children, RR: 1.18 (1.09 to 1.28). In models restricted to specific ethnic groups, we found no consistent differences in any of the associations. CONCLUSIONS The results for NO2 are higher than those published previously. Other studies have reported that the dose-response for PM2.5 may be higher at low concentrations, but less is known about NO2. It is possible NO2 is acting as a proxy for other traffic-related pollutants that are causally related to health impacts. This study underlines the importance of controlling pollution caused by motor vehicles.