Luis Simarro Lacabra (6 January 1851 – 19 June 1921) was a Spanish psychiatrist who was born in Rome while his parents were living in Italy.
He studied medicine in Valencia and Madrid, and in 1877 was appointed director of the Santa Isabel insane asylum at Leganés, outside of Madrid. From 1880 he lived in Paris and studied general anatomy and histology with Louis-Antoine Ranvier and clinical neurology under Jean Martin Charcot. Here he also came under the influence of philosopher Ernest Renan (1823–1892). anatomist Mathias-Marie Duval (1844–1907) and psychiatrist Valentin Magnan (1835–1916). In 1885 he returned to Madrid and opened a private practice, and in 1902 was appointed to the first chair of experimental psychology in Spain.
As a psychiatrist, Simarro was heavily influenced by developments in Germany, particularly Emil Kraepelin's classification and treatment of the insane, Wilhelm Wundt's theory of experimental psychology and Theodor Ziehen's critical analysis of Wundt's approach to psychology.
Notwithstanding his work in psychiatry, Simarro is largely remembered for a contribution made in histology when he developed a silver bromide modification of Camillo Golgi's silver chromate technique. Famed Spanish histologist Ramon y Cajal recognized Simarro's achievement, and mentioned that it was a milestone that allowed him to abandon general histology and to focus on neurohistology.