The theme of this presentation concerns the potential beneficial effects of children's illnesses on their behavioral development. Illnesses of a minor nature such as colds and gastrointestinal upsets are frequent events in the lives of all children at every age, but are most frequent in the preschool period. They are generally not life threatening and are managed within the family, day-care center, or school. These illnesses, like other life perturbations, can expand children's personal and social experiences in ways beneficial to their behavioral development. They provide many opportunities for children to increase their knowledge of self, other, prosocial behavior, and empathy, as well as a realistic understanding of the sick role. This knowledge is gained, not only from their personal feelings and social experiences while ill, but also by their observations of siblings, parents, and peers as they become ill and recover, often in quick succession after their own experience. This important subject has seldom been studied from a developmental point of view. The conceptualizations as presented are based on the author's clinical experiences and the existing related research. It is the author's hope that in the future developmental psychologists, sociologists, anthropologists, and other behavioral scientists will study children's illnesses as part of normal behavioral development.