The history of the concept of anticipation in hereditary disease, the notion that certain hereditary illnesses strike earlier and often more harshly in succeeding generations, reveals that acceptable approaches to heredity varied widely over time and place during the first half of the twentieth century, and that social concerns as well as scientific and medical concepts played an important role in such approaches. This project examined the significant regional and professional variations in the reception and utilization of the concept of anticipation in the study of hereditary disease in Western Europe from 1900 to 1950.