BACKGROUND: This study examines socio-demographic profiles, injecting risk and use of health services among young injectors (15-24) in Albania, Moldova, Romania and Serbia. The objective was to provide age-disaggregated data to identify differences between adolescents (<18) and youth (18-24), and help fill the gap in knowledge on the youngest injectors in this region. METHODS: Cross sectional surveys were conducted in each country using chain-referral sampling to reach diverse networks of people who use drugs (PWID). In Albania and Romania, surveys were conducted in the capitals, respectively, Bucharest and Tirana. Respondents were recruited from 3 cities in Moldova (Chisinau, Balti and Tiraspol) and Serbia (Belgrade, Novi Sad and Nis). Data were collected on risk behaviours, service use and contact with police and other authorities. Analysis focused on associations between unsafe injecting behaviour and key determinants including demographic background, source of needles/syringes, use of harm reduction services and interactions with law enforcement. RESULTS: Although drug use and health-seeking varied across settings, sources of injecting equipment were significantly associated with sharing needles and syringes in Moldova, Romania and Serbia. Obtaining equipment from formal sources (pharmacies, needle-exchange programmes) reduced likelihood of sharing significantly, while being stopped by the police or incarcerated increased it. Adolescents relied on pharmacies more than public sector services to obtain equipment. CONCLUSION: Adolescents comprise a small proportion of PWID in this region, but have poorer access to harm reduction services than older peers. Engaging young PWID through private and public sector outlets might reduce unsafe practices, while use of the justice system to address drug use complicates efforts to reach this population.