BACKGROUND AND OBJECTIVES: Hepatitis C virus (HCV) RNA level in acute HCV infection is predictive of spontaneous clearance. This study assessed factors associated with HCV RNA levels during early acute infection among people who inject drugs with well-defined acute HCV infection. STUDY DESIGN: Data were from International Collaboration of Incident HIV and Hepatitis C in Injecting Cohorts (InC3) Study, an international collaboration of nine prospective cohorts studying acute HCV infection. Individuals with available HCV RNA levels during early acute infection (first two months following infection) were included. The distribution of HCV RNA levels during early acute infection were compared by selected host and virological factors. RESULTS: A total of 195 individuals were included. Median HCV RNA levels were significantly higher among individuals with interferon lambda 3 (IFNL3, formerly called IL28B) CC genotype compared to those with TT/CT genotype (6.28 vs. 5.39logIU/mL, respectively; P=0.01). IFNL3 CC genotype was also associated with top tertile HCV RNA levels (>/=6.3log IU/mL; vs. TT/CT genotype; adjusted Odds Ratio: 4.28; 95%CI: 2.01, 9.10; P<0.01). CONCLUSIONS: This study indicates that IFNL3 CC genotype predicts higher HCV RNA levels in early acute HCV infection.