We sought to define the light microscopic features of eosinophilic folliculitis as it occurs in human immunodeficiency virus (HIV)-infected individuals. The histologic findings of 52 biopsies from 50 patients were graded and compared with six biopsies of suppurative folliculitis from HIV-infected individuals. In all patients, clinical examination showed an eruption of pruritic follicular papules, and the folliculocentric nature of the disorder was confirmed histologically. Perifollicular infiltrates of lymphocytes and eosinophils were identified in all study biopsies, and there was also spongiosis of follicular epithelium. The inflammatory reaction was focused at the level of the follicular isthmus and the sebaceous duct. In all biopsies, lymphocytes and/or eosinophils were present within spongiotic follicular epithelium, but intrafollicular neutrophils were rare. Sebaceous glandular inflammation, eosinophilic pustule formation, and follicular rupture were present in less than half of the biopsies. Small numbers of microbes (bacteria, yeast, Demodex) were identified in 25% of the study biopsies in routine or special stains, but the organisms were away from areas of inflammation and were interpreted as nonpathogenic flora. The biopsies of suppurative folliculitis differed in that neutrophils and macrophages predominated in the infiltrate, microorganisms were readily identified in the inflammatory reaction, and the involved follicle was often ruptured. We believe that eosinophilic folliculitis is a unique HIV-associated dermatosis distinguishable from other folliculitides and papular dermatitides by clinical examination and light microscopy. We present our diagnostic approach.