During the 12^th and 13^th centuries, numerous leprosy hospitals were founded in Europe. Given that leprosy was not considered infectious, this may reflect social dimensions of the disease. Aiming at exploring the impact of leprosy on medieval people and the organisation of the Danish leprosarium at Næstved, we reconstructed the diet of twenty patients using stable isotopes, and compared our results with relevant historical data. The isotope results revealed a terrestrial C₃ diet with a small contribution of aquatic foods. Contrary to historical evidence of daily fish consumption in the leprosy hospital, only six individuals consumed relatively large amounts of freshwater fish. Leprosaria have been considered monastic institutions, and thus a varied diet, poor in aquatic protein, questions the monastic nature of the hospital and points to a social stratification. A multi-isotope analysis of a larger sample set would add to our understanding of the diet of the leprosy patients, as well as their treatment in the leprosarium.