IgG4-related disease (IgG4-RD) is a fibroinflammatory disorder that can affect virtually every organ system. T-helper type 2 responses have been presumed to be pathogenic in this disease, and a high proportion of patients with IgG4-RD are reported to have longstanding allergies, peripheral blood eosinophilia, and serum IgE elevation. It has therefore been proposed that allergic mechanisms drive IgG4-RD. However, no epidemiological assessment of atopy, peripheral blood eosinophilia, and serum IgE concentrations has ever been undertaken in patients with IgG4-RD. In this study, we evaluated these parameters in a large cohort of patients with IgG4-RD in whom a wide range of organs were affected by disease. Our results demonstrate that the majority of patients with IgG4-RD are nonatopic. Nevertheless, a subset of nonatopic subjects exhibit peripheral blood eosinophilia and elevated IgE, suggesting that processes inherent to IgG4-RD itself rather than atopy per se contribute to the eosinophilia and IgE elevation observed in the absence of atopy.