Until the end of the 20th century Forel (1848-1931) was seen as an important neuroanatomist, a fighter against alcoholism, a researcher on ants and the author of Die sexuelle Frage. Forel's racist and eugenic views have been forgotten. Without losing sight of his merits, this article focuses on his attitude to eugenics, and will show that eugenic thinking--based on his main principles--permeated his work.