OBJECTIVES: To explore associations between population density, air pollution concentrations, and related health outcomes in Tāmaki Makaurau Auckland, Aotearoa New Zealand. METHODS: Concentrations of nitrogen dioxide (NO RESULTS: Higher population density was associated with higher concentrations of NO CONCLUSIONS: Higher population density in Auckland is associated with worse air quality and related health outcomes. Motor vehicle traffic is the most important source of pollution and is highest in the most densely populated parts of the city. IMPLICATIONS FOR PUBLIC HEALTH: Housing intensification in Auckland will likely increase ill health from air pollution unless steps are taken to reduce exposure to emissions from motor vehicles.