Leprosy, now largely absent from European consciousness, was a significant social and medical concern in medieval Ireland, and dedicated hospitals, sometimes called lazar houses, were established on the outskirts of towns to separate sufferers from the general population. This one sat just beyond the medieval city proper, a deliberate placement that would have felt familiar to any town in western Europe at the time.

St Stephen's Leper Hospital was founded by the citizens of Dublin in the thirteenth century and endowed with lands at Leopardstown, a name that may itself preserve some memory of the association. At the time of the dissolution of religious houses in the sixteenth century, the complex comprised a church and three stone houses, suggesting a modest but functioning institution rather than a ruin in waiting. The churchyard was walled in 1665, and by 1682 the church had gone out of use entirely. Then, in 1724, Mercers Hospital was constructed on the same ground, a new medical institution layered directly over the medieval one. Excavations carried out in 1991 on the south side of Lower Stephen Street uncovered a wall thought to belong to the medieval hospital complex. A second round of excavations in 1992 on an adjoining plot went further, revealing additional skeletal remains dating from the thirteenth to the nineteenth centuries, as well as foundations of the original medieval buildings.

The site today is urban and well built over, offering little to see at street level. The Mercers Hospital building itself, on Mercer Street Lower, is the visible anchor for anyone trying to orient themselves, though the hospital has long since ceased to operate as such. The excavated material is not on public display, but the 1991 and 1992 digs were significant enough to be written up in the archaeological literature, and anyone with a serious interest in Dublin's medieval topography will find the reports referenced under Hayden, Buckley, and Clarke worth tracking down. The real point of curiosity here is the persistence of a single function across so many centuries, a place set aside for the sick and the dying, long before the Georgians gave it a new name and a new facade.