PIP: The authors define for the purpose of this overview Asia and the Pacific to be the 46 countries and other administrative areas belonging to the Southeast Asia and Western Pacific regions of the World Health Organization. Defined as such, 55% of the world's population lives in the Asia-Pacific region. China, India, and Indonesia, three of the four most populous countries in the world, are part of the region. The region is highly diverse with highly diverse systems in place to monitor the course of the HIV epidemic. This diversity makes it difficult to develop an accurate picture of the epidemiology of HIV and AIDS in Asia and the Pacific. Despite underreporting and data of varying quality, one may reasonably conclude on the basis of available evidence that countries overall in Asia and the Pacific are in a relatively early stage of the HIV/AIDS epidemic. Reported modes of transmission vary widely and include heterosexual sexual contact, homosexual sexual contact, IV drug use, the receipt of blood products, and mother-to-child transmission. A cumulative total of 851,628 AIDS cases had been reported to the World Health Organization (WHO) by December 31, 1993. Reports from the Asia-Pacific region represent 1% of that total. The WHO estimates that there have been more than 3 million AIDS cases and 14 million infections in adults worldwide since the beginning of the epidemic, while other estimates are substantially higher. The Asia-Pacific region accounts for 3% of the estimated AIDS cases, but 15% of the total estimated HIV infections, indicating the relatively recent arrival of the epidemic to that part of the world. The authors discuss HIV case reporting, surveys of HIV prevalence, risk factors for HIV infection, geographic patterns of HIV transmission, molecular and clinical epidemiology, and the future of the HIV epidemic in Asia and the Pacific.