Giuseppe Sergi (1841-1936) was one of the most important anthropologists and psychologists of the age of positivism and this article focuses on three domains of his scientific research: degeneration, eugenics and race. His concept of degeneration is defined as the development of special forms of human adaptation to the environment. This issue is closely related to his theory of the "stratification of character", which had a profound impact on Italian psychiatry and criminal anthropology in the late nineteenth century. Thus, special emphasis is placed on the differences between Sergi and Cesare Lombroso regarding their definitions of criminality and genius. Concerning eugenics, the article analyzes Sergi's key role in the Italian context, discussing his eugenic program based on both repression and education. His remedies against the spread of degeneration included not only radical and repressive measures, but also the improvement of popular education and the living conditions of the working class. In the field of physical anthropology, the article examines Sergi's morphological method of classifying ethnic groups. Although sharply criticized in Italy and abroad, this method had two major effects. First, it led to the definitive split between Sergi and Paolo Mantegazza and to the foundation of the Societá Romana di Antropologia in 1893. Second, it was the starting point for Sergi's theory of Mediterranean "stock", which claimed that European populations were of African origin in contrast to contemporary theories of Aryan supremacy. The article ends with a look at the heated debate over Sergi's Mediterraneanism during the period of Fascism.