Abstract/Text: Alopecia is one of the clinical manifestations of secondary syphilis. It is uncommon for hair loss to be the sole or predominant manifestation, as hair loss is the chief clinical and histologic differential diagnosis of alopecia areata. The main difference between these two entities is the detection of Treponema pallidum in syphilis. We present the case of a 24-year-old Hispanic man, human immunodeficiency virus seropositive in treatment, with tiny patches of non-cicatricial alopecia in the parieto-occipital regions of his scalp. The patient denied previous history of genital or other skin lesions. A biopsy from an alopecic patch was performed which showed an inflammatory non-scarring alopecia with a discrete lymphocytic type inflammatory infiltrate localized in the peribulbar region. There was lymphocyte exocytosis into the matrix, associated with vacuolar degeneration, and scattered apoptotic cells were observed. Plasma cells were scattered. Immunohistochemical studies showed the presence of T. pallidum limited to the peribulbar region and penetrating into the follicle matrix. To the authors' knowledge, this is the first time that spirochetes have been shown in the hair follicle in alopecia syphilitica, suggesting that the spirochetes may be pathogenetic and responsible for the alopecia.