Opioid dependence is a complex and persistent disorder with a high mortality rate and severe impact on health and social situation. It is associated with much harm, including the transmission of blood-borne bacterial and viral infections, self-harm, traumatic injury and drug overdose. All of these harms carry a risk of death, and accordingly, mortality rates in opioid-dependent people are many times higher than those in the general population of the same age and sex. One of the more commonly used strategies for reducing the risks of opioid dependence is the provision of maintenance treatment. In Australia, available maintenance treatments include methadone, buprenorphine, oral naltrexone, and the unregistered sustained-release formulation of naltrexone, naltrexone implants. This thesis reports on a range of data collections and study designs to investigate the levels, predictors and causes of mortality in opioid-dependent persons entering methadone, buprenorphine and naltrexone maintenance treatment in Australia. The studies used data linkage to examine mortality rates and causes of death in a longitudinal cohort of the early entrants to the NSW methadone program, examined the predictors of mortality (particularly the impact of methadone and buprenorphine treatment) using survival analysis in a longitudinal cohort study, compared national mortality rates between methadone, buprenorphine and naltrexone maintenance treatments in a cross-sectional analytic study, and used a small case series of coronial cases to examine whether death from opioid overdose was possible in a recipient of a naltrexone implant. This thesis demonstrates that mortality rates as a whole and from particular causes of death are many times higher in Australian opioid-dependent subjects than the general population, exposure to methadone or buprenorphine maintenance treatment significantly reduced mortality in a sample of opioid-dependent subjects, naltrexone treatment appears to have higher mortality than both methadone and buprenorphine maintenance treatments, and fatal opioid overdose while in receipt of sustained-release naltrexone treatment is possible. These results support longer retention in and repeated access to methadone and buprenorphine maintenance treatments in order to reduce mortality in opioid-dependent people, and greater regulation of the access to and more rigorous monitoring of the mortality associated with oral and sustained-release naltrexone maintenance treatments.