Intravenous drug use (IDU) is driving the HIV epidemic in Russia; over 90% of all HIV-1 infections have occurred within communities of IDUs. In St. Petersburg (population 5 million), the prevalence of HIV infection in IDUs (estimated population 100,000) leapt from 4% in 1999 to 12% in 2000. At present there are an estimated 5-7 million IDUs, a four-fold increase since the end of the Soviet Union. In St. Petersburg, there has been a three-fold increase in regular IDUs and a nine-fold increase in teenage IDUs during the past five years.