In 1995, only one out of 8 national sentinel sites for IDU detected HIV infections. The detected prevalence was 0.02% [14] . By 1997, 3 out of 22 sites detected positives, and the average prevalence increased to 6.6%. After that, national average HIV prevalence among IDUs varied between 5.4% and 8.2% [15, 22] . However, dramatic geographic differences in HIV prevalence have been observed. Yunnan and Xinjiang provinces have the most severe HIV infection rates among IDUs. Other provinces along or close to drug trafficking roads, such as Guangxi, Sichuan, Guizhou, Hunan, and Jiangxi, have moderate epidemics [25] . HIV began to spread rapidly in Yunnan province in the late 1980s and early 1990s [26] . High prevalence among IDUs was first detected in 1998 in Urumqi City (28.8%) and in Yining City (82.2%) of Xinjiang Province and later on in selected sentinel sites for IDU in other provinces [27] . These include Guangxi (>10%, 1998 sentinel data), Jiangxi (14.5%, 2000), Sichuan (16-20%, 2002) , Guizhou (17-19%, 2002) , and Hunan (15-20%, 2003) [23] . In 2004, 75% of HIV national sentinel sites for IDU detected HIV infection. More than 20% of HIV prevalence was reported in selected sites in Xinjiang, Sichuan, Guizhou, Guangxi and Hunan [22] . Official HIV prevalence rates in other geographic areas remain <10%; these reports may reflect reality or may be due to failure in detection.