Instituto Leprológico de Trillo [Trillo Institute of Leprosy] was installed on the site of an eighteenth century spa, which was famous in the area for the healthy properties of the waters from the wells. These waters were recommended for many diseases such as the scrofula, rheum, leprosy, and others.

In 1770 King Carlos III opened the spa, which enjoyed a great deal of popular success. For more than one century, many patients took the waters, and in 1872, the spa was renovated and enlarged so as to admit thousands of patients. However, the decline in popularity of this sort of center during the twentieth century and the effects of the Spanish Civil War ensured that it was abandoned during the 1940s.

Probably, the increase of cases of leprosy in the Spanish post-war years, and the requirement for a sanitary center requiring a minimum economic investment, made possible the opening of this leprosy sanatorium in December, 1943.

Its activities as a leprosy hospital came to an end in 1996, when only 30 leprosy patients, whose average age was 69 years and who had spent, on average, 35 years there, remained.

El Instituto Leprologico de Trillo lodged patients of a very diverse derivation, so when it closed, those who were still there came from Andalucia (19), Extremadura (2) Galicia (2), Valencia (2), Castilla-La Mancha (1), Castilla y Leon (1), Asturias (1), Marruecos (1) y Filipinas (1).