Traveling to underdeveloped countries requires several important preventive measures, such as vaccination and bringing electric water boiling apparatus. After arriving in the underdeveloped country, travelers must avoid unheated water, ice, beverages containing ice, raw vegetables, fruits cut by local people. However, many Japanese travelers do not pay attention to these points, resulting in increasing numbers of cases of tropical diseases such as cholera, dysentery, giardiasis, among orally contracted intestinal diseases. We must learn from Americans and British who are very cautious in traveling to these areas. In addition to educating travelers about preventive measures, doctors who will see patients returning from traveling in underdeveloped countries must be able to recognize and treat tropical diseases. Unfortunately, this is often not the case in Japan, causing delays in diagnosis and treatment. It is imperative to diagnose communicable diseases as quickly as possible to avoid unnecessary secondary infections. Thus, for a traveler accumulating knowledge on the current hygienic conditions in the tropical country must also be one of the necessary preparations.