The unprecedented scale and speed of contemporary international travel means that ever increasing numbers of travellers are exposed to unfamiliar infections and other hazards. Since 1973, surveillance has been conducted at the Communicable Diseases (Scotland) Unit on illnesses affecting returning travellers. This has helped define the perspective of illness associated with travel, to evaluate the effectiveness of pre-travel health advice and to develop a computerised data base designed to give advice on the prevention of travellers' illnesses. These and other epidemlological studies suggest that: (a) younger travellers experience more illness (b) the greater the climatic and cultural contrast between the traveller's country of origin and the destination country, the higher the risk (c) by far the commonest afflictions the traveller is likely to experience are diarrhoea and vomiting (d) the cost of travel-related illness in the UK is in excess of £11 million.