What you don't want is an illness. A team of doctors in Nepal, Germany and the US have tracked diseases brought home by travellers visiting developing countries and the most common were fever illnesses (malaria, dengue fever etc), diarrhoeal illnesses caused by parasites; skin disorders caused by insect bits and gastrointestinal disorders such as liver infection. The data came from 30 specialised clinics in six developing regions in the world. Take some preventative measures by visiting the Centre for Disease Control and Prevention's excellent website. Here you'll find information on destinations all around the world, vaccinations required and other tips.