We describe recent trends in the HIV epidemic and the differences between eastern and central Europe, using surveillance data, and published and unpublished reports. During the past 5 years, most countries of the former Soviet Union have been severely affected by HIV epidemics that continue to spread as a result of injecting drug use. With an estimated 1 million individuals already infected--mostly injecting drug users--and high rates of syphilis, the region may soon also face a large-scale epidemic of sexually-transmitted HIV infection. Indeed, data indicate that an HIV epidemic, fuelled by heterosexual transmission, is emerging; its expansion will depend on the size of so-called bridge populations that link high-risk groups with the general population. The lack of evidence to indicate increased rates of HIV as a result of homosexual transmission could indicate the social vulnerability of homosexual and bisexual men in the region rather than the true epidemiological picture. In view of the current levels of HIV prevalence, eastern Europe will soon be confronted with a major AIDS epidemic. By contrast, rates of HIV in central Europe remain low at present, but behaviours that promote HIV transmission are present in all countries. Improved measures to prevent further HIV spread are urgently needed.