Indonesian Hajj Cohorts and Mortality in Saudi Arabia from 2004 to 2011.

The Hajj is an annual pilgrimage that 1-2 million Muslims undertake in the Kingdom of Saudi Arabia (KSA), which is the largest mass gathering event in the world, as the world's most populous Muslim nation, Indonesia holds the largest visa quota for the Hajj. All Hajj pilgrims under the quota system are registered in the Indonesian government's Hajj surveillance database to ensure adherence to the KSA authorities' health requirements. Performance of the Hajj and its rites are physically demanding, which may present health risks.