Transthyretin (TTR), a well-established nutritional marker, was measured in patients with active and inactive celiac disease (CD) in order to assess its value as a marker of disease activity. CD activity was assessed by intestinal biopsy to determine intestinal atrophy histologically and by measuring the level of antiendomysial antibody titer. TTR was measured in 26 CD patients fed a diet containing gluten and 22 CD patients fed a gluten-free diet. The control group was composed of 65 healthy sex- and age-matched children. We compared the TTR levels to the two established markers of CD activity. TTR levels were lowest among the celiac patients fed a diet containing gluten and differed significantly from those of the other two groups (r = 0.7, p < 0.002). The TTR levels correlated inversely with both the degree of mucosal atrophy (r = 0.6, p < 0.005) and with anti-endomysial antibody titers (p < 0.005). TTR levels appear to be correlated with morphologic and serologic markers of activity in celiac patients. TTR can be used as a systemic parameter in assessing celiac patients. It can contribute information to the evaluation of children in whom celiac disease is suspected, and it can monitor patients' diet compliance.