This study explores factors associated with early adolescent (aged < or = 16 years) initiation into injection drug use among young (< or = 29 years) injection drug users (IDUs). Data were collected through the Vancouver Injection Drug Users Study (VIDUS). Since 1996, 542 participants aged 29 years and younger have been enrolled and followed. In total, 205 (38%) young participants were initiated at age 16 years or younger. The proportion of young initiators was greater among: females, adjusted odds ratio [AOR]: 1.63 (95% confidence interval [CI]: 1.09-2.44); sex workers, AOR: 1.61 (CI: 1.11-2.31); binge drug users, AOR: 1.45 (CI: 1.01-2.08); and those who have been in juvenile detention or jail, AOR: 1.78 (CI: 1.16-2.66). Early initiates were more likely to be infected with human immunodeficiency virus (HIV), OR: 2.6 (CI: 1.3-5.0) and hepatitis C virus (HCV), OR: 2.6 (CI: 1.3-5.0). Targeted early interventions are required, specifically designed for and in collaboration with girls and young women.