The potential for spread of infectious diseases associated with mass gatherings is well recognised. Hajj, the unique annual mass gathering of over 2 million Muslims from all over the world, presents enormous challenges to the authorities in Saudi Arabia. They have a comprehensive programme updated annually, to ensure that all aspects of Hajj rituals are conducted safely and without major incident. The inevitable overcrowding in a confined area of such large numbers increases the risk of respiratory infections. Of these 'Hajj cough' is the most frequently reported complaint and is caused by a variety of viruses and bacteria. The outbreaks of meningococcal W135 strains in 2000 and 2001 with the associated high mortality showed the potential for international spread at mass gatherings. Collaboration between health policy makers and community leaders in the UK resulted in a rapid and impressive reduction of these infections. On-going disease surveillance and data analysis is necessary to better understand health risks and strengthen evidence base for health policy and prevention. The battle against spread of travel-related infections is a shared responsibility. Countries sending pilgrims should co-ordinate preventive measures by healthcare professionals and community groups. A multi-pronged approach involving awareness programme for pilgrims and their health advisers, supported by rapid diagnosis, timely treatment, prevention by vaccine, community measures, infection prevention and control practices are necessary. The benefits from such measures go beyond the Hajj to protect health and reduce inequalities. Establishing an international centre for public health relating to the Hajj will enable co-ordinating international health action and appropriate intervention.