Background: The histopathologic diagnosis of chilblains is controversial and the histologic changes are often considered nonspecific, mainly because they are poorly documented. Although a dermal inflammation in chilblains has been noticed, the infiltrate has not yet been characterized. Objective: Our purpose was to analyze microscopic and immunohistochemical findings in a large series of chilblains and to compare the results with those of lupus erythematosus (LE). Methods: We included 36 cases of clinically typical chilblains of the hands, of which 17 were thoroughly investigated to rule out cryopathy or LE. Ten biopsy specimens of hand lesions from patients with proven LE were included as controls. All slides were analyzed by conventional microscopy and by immunohistochemistry with anti-CD3, anti-CD20, and anti-CD68 antibodies. Results: The most characteristic finding in chilblains (47% of cases) was the association of edema and reticular dermis infiltrate that showed a perieccrine reinforcement. Such a combination of changes was not observed in LE. Epidermal changes in chilblains consisted mainly in necrotic keratinocytes in 52% of cases. The comparison of 17 idiopathic chilblains with LE showed significant differences in spongiosis (58% vs 0% respectively), vacuolation of basal layer (6% vs 60%), edema of the dermis (70% vs 20%), and deep perieccrine inflammation (76% vs 0%). Immunohistochemistry showed that the infiltrate was composed of a majority of T cells associated with macrophages and a few B lymphocytes. The same pattern was observed in both chilblains and LE. Conclusion: Our results show that a predominantly T-cell papillary and deep infiltrate with a perieccrine reinforcement, associated with dermal edema and necrotic keratinocytes, are the hallmarks of chilblains of the hands. These changes can help differentiate idiopathic perniosis from LE; immunohistochemistry is of no use in differentiation. (J Am Acad Dermatol 2001;45:924-9.)