The term "Western diseases" refers to those conditions that are rare or absent in underdeveloped areas of the Third World and increase in frequency with adoptions of Western customs. In adults, they include such common conditions as coronary artery disease, essential hypertension, appendicitis, cholesterol gall stones, and colon cancer. The best examples of Western diseases in the pediatric population are asthma, allergies, appendicitis, and inflammatory bowel disease. Limited data from sub-Saharan Africa suggest other pediatric surgical conditions may fall into this category, including hypertrophic pyloric stenosis, gastroesophageal reflux, perirectal abscess, anal fissure, gastroschesis, and neuroblastoma. Existing theories for the origins of Western diseases have postulated a role for decreased dietary fiber, improved hygiene, fetal programming, and a protective effect of tropical enteropathy. How these factors might relate to the rise of appendicitis, inflammatory bowel disease, and possibly other common pediatric surgical diseases in industrialized societies remains poorly understood. Further research is needed to better define geographical differences in common pediatric surgical conditions and to investigate how genetic and environmental factors interact to modify risk of disease. Understanding the molecular mechanisms that give rise to Western diseases could lead to new therapeutic and prevention strategies for some of the most common pediatric surgical conditions in industrialized countries.