To determine whether the self-reported personal wellbeing of a cohort of people who inject drugs (PWID) changes over time, and to identify longitudinal correlates of change.We used Personal Wellbeing Index (PWI) scores reported between April 2008 and February 2015 by 757 PWID (66% male) enrolled in the Melbourne Injecting Drug Use Cohort Study (2,862 interviews; up to seven follow-up waves). A mixed-effects model was used to identify correlations between changes in temporal variables and changes in individual PWI scores while controlling for demographic variables.The cohort's mean PWI score did not significantly differ over time (between 54.4/100 and 56.7/100 across the first four interview waves), and was 25-28% lower than general Australian population scores (76.0/100). However, there were large variations in individuals' PWI scores between interviews. Increased psychological distress, moving into unstable accommodation, reporting intentional overdose in the past 12 months and being the victim of assault in the past six months were associated with declines in PWI scores.Participants experienced substantially lower levels of personal wellbeing than the general Australian population, influenced by experiences of psychological distress, assault, overdose and harms related to low socioeconomic status. The results of this study suggest a need to ensure referral to appropriate housing and health support services for PWID.