Background: Recently a new polyomavirus was identified in a patient with trichodysplasia spinulosa (TS), a rare follicular skin disease of immunocompromised patients characterized by facial spines and overgrowth of inner root sheath cells. Seroepidemiological studies indicate that TSPyV is ubiquitous and latently infects 70% of the healthy individuals. Objective: To corroborate the relationship between active TSPyV infection and TS disease by analyzing the presence, load, and precise localization of TSPyV infection in TS patients and in controls. Study design: TS lesional and non-lesional skin samples were retrieved from TS patients through a PubMed search. Samples were analyzed for the presence and load of TSPyV DNA with quantitative PCR, and for expression and localization of viral protein with immunofluorescence. Findings obtained in TS patients (n= 11) were compared to those obtained in healthy controls (n= 249). Results: TSPyV DNA detection was significantly associated with disease (P<0.001), with 100% positivity of the lesional and 2% of the control samples. Quantification revealed high TSPyV DNA loads in the lesional samples (∼10 6copies/cell), and low viral loads in the occasionally TSPyV-positive non-lesional and control samples (<10 2copies/cell). TSPyV VP1 protein expression was detected only in lesional TS samples, restricted to the nuclei of inner root sheath cells over-expressing trichohyalin. Conclusions: The high prevalence and load of TSPyV DNA only in TS lesions, and the abundant expression of TSPyV protein in the affected hair follicle cells demonstrate a tight relation between TSPyV infection and TS disease, and indicate involvement of active TSPyV infection in TS pathogenesis.