Between about 1900 and 1940 there were dozens of recorded incidents in the United States, and extreme cases occurred almost as frequently as they have done in the last two decades. This article describes and attempts to classify incidents of serial homicide in this area. It also discusses the changing theoretical and medical explanations used to account for this type of crime and the impact of new theories on the practice of the courts and law-enforcement agencies. Finally, the frequency of serial homicide is tentatively linked to the broader social and economic history of the period. 2 tables, list of serial murder cases for 1971-1988, 75 references. (Author abstract)