The sanatorium of Fontilles is located in the municipality of La Vall de Laguar, on the southern slope. The toponym Fontilles seems to derive from the abundant springs that exist in the valley, which belong to the aquifer of El Penyó, among which stands out the spring of El Castellet, which together with others supplies the sanatorium with the necessary water.

The sanatorium of Fontilles is historically linked to the disease of leprosy. Faced with the evolution of leprosy, at the beginning of the 20th century, the sanatorium was set up to treat patients affected by the disease. The origins of the sanatorium date back to 1901. According to El Diari del Col·legi-Noviciat de la Companyia de Jesús a Gandia, Jesuit Father Carlos Ferris i Vila, native of Albal (Valencia), went to the town of Tormos on the 10th of December, 1901, to preach a six-day mission. The missionary stayed at Mr Joaquim's house. In the adjoining house lived Bautista Perelló, a patient suffering from leprosy. The constant lamentations of the patient moved the Jesuit and encouraged him to create a leprosarium.

The most recent hospitalisation data available refers to 2002, when 68 patients resided in Fontilles. Currently, the health activity concerning leprosy focuses on the health care of the sick residents, on the training of personnel and on the investigation of the disease and its treatment. Likewise, and given the considerable reduction in the number of patients, the institution of Fontilles has considered attending to other social needs.