The HIV epidemic in Russia has grown significantly in the past 5 years, primarily due to injection drug use. An estimated 1 million people are HIV-infected in Russia, but very few people are treated with highly active antiretroviral therapy (HAART). We developed a dynamic epidemic model to evaluate the effect and cost-effectiveness of treating HIV-infected injection drug users (IDUs) and non-IDUs with HAART. We find that exclusively treating IDUs provides greater health benefit at less total cost, than exclusively treating non-IDUs. However, treatment of both IDUs and non-IDUs is very cost-effective. Our findings highlight the urgency of initiating HAART for both IDUs and non-IDUs in Russia.