INTRODUCTION: Although people with serious mental illness (SMI) have a high prevalence of physical illness, health-related quality of life (HQoL) has not been sufficiently explored. AIM: To explore the self-reported HQoL of mental health service users in New Zealand. METHODS: Responses on the Medical Outcomes Study 36 Item Short Form (SF-36) measure of HQoL from 404 adult mental health service users in a metropolitan district health board area in New Zealand were analysed and compared to a representative sample of the general population. RESULTS: Mental health service users scored significantly lower on all eight domains of the SF-36 than the general population, the largest difference being in the role limitation — emotional domain. DISCUSSION: Being female, younger than 25, obese or overweight, or of New Zealand European/Other ethnicity were associated with poorer functioning on multiple HQoL domains. Future studies should seek to understand the factors contributing to perceptions of HQoL of mental health service users in New Zealand.