Mental illness is the third highest cause of poor health in New Zealand, accounting for 11% of the total burden of disease. Like many other chronic illnesses, associations between mental health outcomes and the built and social environment have been found. Roads and traffic have been associated with reduced mental wellbeing as they are a source of stress for individuals and are disruptive to daily activities; partially a result of the air and noise pollution produced. The primary aim of this research was to investigate the relationship between exposure to traffic and mental health treatment in Auckland, New Zealand. Measures of distance to motorways, road class metrics, traffic volume and traffic density were produced for all households in Auckland. Poor mental health for individuals was measured by cases of issued prescriptions for mood and anxiety disorders or use of addiction related services in a 12-month period, sourced from the Ministry of Health Programme for the Integration of Mental Health Data (PRIMHD). A random sample of Auckland address points were selected for comparison. Logistic regression was used to investigate possible associations. The social composition of neighbourhoods were considered as confounders, including income, deprivation and social capital indicators. The effect of green space was also investigated. No detectable effect of traffic volume or traffic density on mental health was found. However, the volume of heavy commercial vehicles was associated with poor mental health, with a 3% increase in treatment for every 1000 vehicles on motorways within 100 metres of home address points. The neighbourhood has an important influence on mental health outcomes; deprivation and indicators of social capital are among the strongest predictors, but they also predicted exposure to traffic. Controlling for these confounders, the effect of heavy commercial vehicles on motorways decreased to 1% increase in treatment per 1ooo vehicles. This research provides a useful contribution to the literature investigating traffic and mental health due to the geographic scale at which it is performed, and the use of individual exposure and health measures.