In 2007, an estimated 700,000 persons in China were living with human immunodeficiency virus (HIV) infection. An estimated 50,000 new HIV infections and 20,000 deaths related to acquired immunodeficiency syndrome (AIDS) occurred in 2007, and an estimated 71% of persons with HIV infection were unaware of their HIV status. In 2007, 40.6% of those living with HIV had been infected through heterosexual transmission and 38.1% through injection-drug use. Guangdong Province in southeastern China is the country's most populous province, with an estimated 75.6 million permanent residents and 16.5 million migrants; the province has undergone rapid economic development. Since 1986, a case-based surveillance system (CBSS) in China has collected data on persons infected with HIV, including demographic characteristics and transmission categories. To assess recent trends in HIV infection in the province, the Guangdong Center for Disease Control, with technical assistance from CDC, analyzed CBSS data for the period 1997--2007. The results of that analysis indicated that the number of HIV cases increased from 102 in 1997 to 4,593 in 2007, although this increase resulted, in part, from expanded testing and surveillance. Among males classified by HIV transmission category, 82.1% of newly diagnosed infections were attributed to injection-drug use. Among females classified by HIV transmission category, 53.7% engaged in high-risk heterosexual conduct. Despite substantial methodologic limitations, these results can be useful to Guangdong public health agencies in targeting and evaluating HIV prevention, care, and treatment programs.