Folliculitis decalvans (FD) is a rare variant of primary cicatricial alopecia, for which the etiopathogenesis remains unclear. Our purpose was to evaluate whether certain immunologic mechanisms might have a significant role in the pathogenesis of FD. Lesional scalp biopsy specimens from 7 patients with FD, 7 with lichen planopilaris, and 4 with alopecia areata were studied immunohistochemically by using monoclonal antibodies to CD1a, CD3, CD4, CD8, CD20, CD25, HLA-DR, interleukin (IL)-1beta, IL-4, IL-8, interferon gamma, tumor necrosis factor alpha, basic fibroblast growth factor (b-FGF), transforming growth factor (TGF)-beta, endothelial leukocyte adhesion molecule 1, intercellular adhesion molecule (ICAM)-1, and vascular cell adhesion molecule. We showed that early FD lesions are characterized by an infiltration of activated T-helper cells, featuring mixed TH1/TH2 polarization. IL-8 and ICAM-1 may contribute to the infiltration of neutrophils, whereas b-FGF and TGF-beta may represent important mediators of the fibrosis that characterizes late-phase FD.