The UNAIDS/WHO Working Group on HIV/AIDS/STI Surveillance updated its Estimating the Size of Populations at Risk for HIV report. The report synthesizes the "state of the art" practices of many countries in population size estimation.

The updated report includes new material that has surfaced since the original workshop was held in Bali, Indonesia, in April 2002.

Estimating the Size of Populations covers the major methods available for population size estimation, with their strengths and weaknesses, and gives examples. It also explores how best to choose the right method for a given country situation and sub-population. The document also provides modified copies of the exercises used during the Asian workshop.

The report, however, is not intended as a comprehensive guide to population size estimation: more thorough tool kits will be needed and for some sub-populations may already be available.