INTRODUCTION: There are limited data on young people who inject drugs (PWID) from low- and middle-income countries where injection drug use remains a key driver of new HIV infections. India has a diverse injection drug use epidemic and estimates suggest that at least half of PWID are ≤30 years of age. We compared injection and sexual risk behaviours and HIV incidence between younger and older PWID and characterized uptake of HIV testing and harm reduction services to inform targeted HIV prevention efforts. METHODS: We analysed cross-sectional data from 14,381 PWID recruited from cities in the Northeast and North/Central regions of India in 2013 using respondent driven sampling (RDS). We compared "emerging-adult" (18 to 24 years, 26% of sample) and "young-adult" PWID (25 to 30 years, 30% of sample) to older PWID (>30 years, 44% of sample) using logistic regression to evaluate factors associated with three recent risk behaviours: needle-sharing, multiple sexual partners and unprotected sex. We estimated age-stratified cross-sectional HIV incidence using a validated multi-assay algorithm. RESULTS: Compared to older adults, emerging-adults in the Northeastern states were significantly more likely to share needles (males adjusted odds ratio [aOR] 1.82; females aOR 2.29, p < 0.01), have multiple sexual partners (males aOR 1.56; females aOR 3.75, p < 0.01), and engage in unprotected sex (males aOR 2.29, p < 0.01). In the North/Central states, young-adult males were significantly more likely to needle-share (aOR 1.23, p < 0.05) while emerging-adult males were significantly more likely to have multiple sexual partners (aOR 1.74, p < 0.05). In both regions, emerging-adults had the lowest HIV testing. Participation in harm reduction services was low across all age groups. Annual HIV incidence was higher in emerging- and young-adult PWID in the North/Central region: emerging-adults: 4.3% (95% confidence interval [CI] 3.0, 5.6); young-adults: 4.9% (95% CI 3.7, 6.2); older adults: 2.1% (95% CI 1.4, 2.8). CONCLUSIONS: Higher HIV incidence and engagement in risky behaviours among younger PWID compared to older PWID, coupled with low utilization of harm reduction services highlight the importance of targeting this population in HIV programming. Age-specific interventions focused on addressing the needs of young PWID are urgently needed to curb the HIV epidemic in this vulnerable population.