Worldwide there is an increasing prevalence of psychological disorders. Despite this, research has indicated few people ever use mental health services or receive treatment. Exploration of mental health service use has shown it to be complex and influenced by many personal as well as structural factors. The New Zealand research is limited in its comprehensive examination of the causative factors regarding use of mental health services. It is for this reason that this thesis examined patterns and predictors of mental health service use by using an expanded version of Andersen's Behavioural Model of Health Care Utilisation. This framework enabled a comprehensive exploration of the nature and extent of formal and informal mental health service utilisation in the lower North Island of New Zealand. The results indicated that informal help was used more than formal mental health services. The highest users of mental health services were the least satisfied. Furthermore, the most significant predictors of formal utilisation were having a positive attitude towards mental health services: being female; identifying as Māori; possessing a Community Services Card; and perceived psychological need. However, it emerged that availability of services was the predominant barrier to formal mental health use. In conclusion, the current findings show that certain groups are more likely to utilise a higher frequency of services than other community groups. This suggests mental health services are not distributed equally among communities in the lower North Island of New Zealand. Furthermore, the importance of availability as a predictor of service use indicates that improvements are required at the structural level of the mental health system.