The article analyses the significance of the concept of "obsession" in nineteenth-century alienism. From a clinical point of view, Esquirol's description was completed by other authors (Jules Falret, Legrand du Saulle). In the area of psychopathological studies, French alienism, with Morel's emotional delirium or Janet's psychasthenia, defended the emotional theory, as opposed to the intellectual disorder proposed by German doctors. Lastly, the importance of the cultural framework is stressed in the appearance of obsessive symptoms and their interpretation. Along these lines, the article discusses the relationship of religious scruples to melancholy or the appearance of diagnostic categories subject to fin de siècle codes and mentalities.