HIV/AIDS has emerged as a grave public health threat in Central and Eastern Europe and in the Central Asian republics over the past five years. Massive political, social, cultural, and behavioural changes - along with economic upheaval and collapse of the public health infrastructure in many countries - have created circumstances conducive to the rapid spread of HIV. This paper reviews HIV and sexually transmitted disease (STD) data for all countries in the region, as well as behavioural, social, cultural, and other HIV epidemic enabling factors. The epidemiological picture of HIV in the region is mixed. Russia, Ukraine, Moldova and Belarus already have advanced epidemics. Some other countries in the region share similar enabling factors and have seen a very high proportion of their total number of HIV infections detected in only the past 18 months, indicating the emergence of recent epidemics. Several countries are more stable in their HIV incidence. Behavioural studies indicate that risky sexual and injection related practices are common in many vulnerable populations. HIV prevention steps, if taken quickly enough and on a large scale, can limit the scope of the HIV epidemic that is now unfolding in Central and Eastern Europe. This will require new models of government/non-governmental organization cooperation, policy approaches for addressing structural factors underlying the epidemic, and attention to human rights protection.