People who inject drugs (PWID) typically do so over considerable periods, in some cases up to 20 or 30 years, before stopping for a sustained period (Oppenheimer et al. 1994, Henderson et al. 2002). One aim of drug law enforcement and harm reduction interventions is to reduce the negative health and social consequences experienced by PWID and society during the period in which an individual injects drugs, which is sometimes called their ‘injecting career’ (Ministerial Council on Drug Strategy 2011). The term ‘maturing-out’ has long been applied to people who use drugs but then outgrow their habits (Winick 1962), whether with the aid of services or of their own accord. Little is known about whether PWID in Australia mature out of drug use in the longer term, and how this is achieved. Prospective cohort studies such as the Melbourne Injecting Drug User Cohort Study (MIX) (Horyniak et al. 2013) offer an insight into these patterns. This paper considers some of the changes that have been observed in the MIX cohort of PWID over time.