Injecting drug use is a persistent behaviour that increases the risk of morbidities and mortality. We assessed the burden of hospital separations among people who inject drugs (PWID), the excess compared to the general population and characteristics of separations associated with frequent use.

Prospective cohort study.

All public and private hospitals in Victoria.

757 community-based PWID with hospital separations between January 2008 and June 2013 identified through record linkage, who contributed over 3729 person-years.

Counts, proportions and rates of hospital separations, descriptive administrative data including all diagnoses, comparison of separation rates to the general population, trend in separations and factors associated with frequent separations.

There were 2106 separations in the cohort. The most common principal diagnoses were related to mental and behavioural disorders (31%), but social circumstances influencing health was the most common group of diagnoses (61%) when all contributing diagnoses for each patient were considered. Separation rates were up to three times higher than in the age-matched population, and there was a 12% increase in separations every 6 months. Over a quarter (29%) of the cohort had frequent separations (defined as two or more separations in a calendar year), which were associated with mental health-related diagnoses, being discharged to locations other than a patient's residence, having a medical as opposed to surgical intervention, seasonal patterns, relationship status and gender.

Mental health conditions and other characteristics associated with separations and frequent separations in particular, emphasise the importance of providing referrals to harm reduction, social services and mental health services at discharge in order to reduce excess hospital separations among PWID.