Stable isotope analysis in the reconstruction of human palaeodiets can yield clues to early human subsistence strategies, origins and history of farming and pastoralist societies, and intra- and intergroup social differentiation. In the last 10 years, the method has been extended to the pathological investigation. Stable isotope analysis to better understand a diet-related disease: celiac disease in ancient human bones was carried out. To do this, we analyzed the nitrogen and carbon isotopic composition of human (n = 37) and faunal (n = 8) bone remains from the archaeological site of Cosa at Ansedonia, on the Tyrrhenian coast near Orbetello (Tuscany), including the skeletal remains of a young woman (late 1st century–early 2nd century Common Era [CE]) with morphological and genetic features suggestive of celiac disease. We compared the young woman's isotopic data with those of other individuals recovered at the same site but from two later time periods (6th century CE; 11–12th century CE) and with literature data from other Italian archaeological sites dating to the same period. Her collagen δ13C and δ15N values differed from those of the samples at the same site, and from most but not all of the contemporary sites. Although the woman's diet appears distinct, chronic malnutrition resulting from severe malabsorption of essential nutrients due to celiac disease may have affected the isotopic composition of her bone collagen. Am J Phys Anthropol 154:349–356, 2014. © 2014 Wiley Periodicals, Inc.