This article examines the influence of the French alienist Alexandre Brierre de Boismont in the first development of the Spanish psychiatric profession during the third quarter of the 19th century. As an outstanding figure of French psychological medicine, Brierre enjoyed great scientific prestige among Spanish doctors, but he also took an active part in promoting and legitimizing the cause of alienism in Spain. For instance, he was involved in projects for the reform or creation of new mental hospitals, supported the admission of some Spanish colleagues into the Société Médico-Psychologique and made a decisive contribution to the social recognition of the professional and medico-legal expertise of alienists in Spain. His case is thus an excellent example of the important role played by international relations and the scientific and professional networks of European alienism in spreading the discourses and practices of the emerging psychological medicine.