To detect acute HIV infections (AHIs) in real time among people who inject drugs (PWID) in St. Petersburg, Russia and to test the feasibility of this approach. Prospective cohort study. One hundred seronegative or acutely HIV-infected at screening PWID were enrolled and followed until the end of the 12-month pilot period. Each participant was evaluated, tested, and counseled for HIV monthly. Two HIV tests were used: HIV antibody and HIV RNA PCR. If diagnosed with AHI, participants were followed weekly for a month; then, monthly for 3 months; and then, quarterly for the duration of the follow-up period. HIV risk behavior was assessed at each study visit. Most enrolled PWID were 30-39 years old, male, completed high school or more, not employed full-time, heroin users, and frequently shared injection paraphernalia. AHI prevalence at screening was 1.8% [95% confidence interval (CI): 0.4, 5.5]. Three participants with AHI at enrollment represented 3% (95% CI: 0.6, 8.5) of the 100 participants who consented to enroll. Among the HIV-uninfected participants (n = 97), the AHI incidence over time was 9.3 per 100 person-years. Persons with AHI were more likely to report alcohol intoxication within the prior 30 days. This was the first study to detect AHI using a cohort approach. The approach proved to be feasible: recruitment, retention, AHI detection, and virological endpoints were successfully reached. A cost analysis in a real-world setting would be required to determine if this strategy could be brought to scale. The study revealed continued high HIV incidence rate among PWID in St. Petersburg, Russia and the importance of prevention and treatment programs for this group.