Background All youth in Sri Lanka are not at risk of HIV/AIDS. However, certain socio-economic and behaviour factors are present among youth which make them vulnerable. There are subsets of especially vulnerable youth (EVY) and most-at-risk youth who need to be identified for targeted interventions. Identification of types of subsets and size are essential for interventions. The Objective of this is to identify the subsets of EVY and estimate the size according to the geographical area in the Western Province,

Method Groups of EVY in the western province were identified using participatory approach with broad based consultation of various stakeholders in the public, private and civil society organisation including youth organisations.

Geographic mapping and size estimation was done using the participatory method in group consensus with the key partners. Previous studies, ad hoc surveys, programmatic data from the various organisations including census and statistic data, and experience of the participants were used.

Series of mapping workshops conducted to finalise the locations and size of the population groups identified as EVY. This was done interactively within each group of experts assigned to each study zone. Locations were marked as a point layer manually on Topographic maps. Each point was assigned a definite number relevant to the size.

Results Ten number groups of EVY were identified with total of 47,285 in the Western Province. Final results were generated by using the topographic maps of the Western Province. These maps were then scrutinised carefully in a systematic way to read the locations and the number of the population group marked by group ID. Different point layers for each identified EVY was created on digital topographic maps.

Conclusion Ten groups of EVY were identified according to the size and geographical areas. These data will be using future HIV prevention interventions with different approaches.