The first reported filovirus outbreak occurred in August 1967, when laboratory workers in Marburg and Frankfurt, Germany, and Belgrade, Yugoslavia (now Serbia) became infected with an unknown highly pathogenic agent. The disease was characterized by high fever, malaise, rash, hemorrhagic and tetanic manifestations, and high lethality, amounting to 25%. The disease was introduced to Europe by grivets (Chlorocebus aethiops), which were used for biomedical research and vaccine production. The causative agent, Marburg virus, was isolated and identified by scientists of the University of Marburg, Germany in cooperation with specialists for viral electron microscopy at the Bernhard Nocht Institute in Hamburg, Germany. In this chapter, Dr. Slenczka, who was involved in the first isolation of Marburg virus in 1967, describes the desperate hunt of the causative agent of this first filovirus disease outbreak in the center of Europe, its successful isolation, the likely route of transmission from a monkey trading station to vaccine production facilities in Germany and Yugoslavia, and the consequences of this outbreak, including a shortage in the production of poliomyelitis vaccine In addition, this chapter provides insight into some of the peculiarities of filovirus infection, such as sexual virus transmission several months after recovery and the role of Ca2+-loss in Marburg virus pathogenesis, which were already observed during this first well-documented Marburg virus disease outbreak.