As is well known, Gregorio Marañón and Posadillo (1887-1960) played a key role in the birth of Endocrinology in Spain. However, her medical work also focused on other important areas. It was above all in the 1910s and 1920s that Marañón focused his attention on the social and health situation in Madrid, probably linked to his professional link to the treatment of infectious diseases, since he took over the Infectious Diseases Chamber of the Madrid General Hospital since 1911, where he had the opportunity to treat this type of patient. As a result of her concern about the social aetiology of over-prevalent diseases or epidemic outbreaks, in the following years, she published a number of specialised articles and submitted communications to the Royal National Academy of Medicine on these issues linked to the country’s social and health situation. This work seeks to study this less well known aspect of Gregorio Marañón’s work.