Xeroderma pigmentosum lesions related to ultraviolet transmittance by clothes. Xeroderma pigmentosum is associated with severe actinic degeneration of the skin. Our patient with xeroderma pigmentosum showed increasing actinic damage in some areas covered by clothes. We therefore performed a complete evaluation of the patient's exposure to ultraviolet radiation. This included transmission measurements of the patient's clothes, glasses, and car windows. The transmission of UVB (280 to 320 nm) by the clothes varied from none to 17.8%. The transmitted UVB radiation was proportional to the clinical manifestations of xeroderma pigmentosum. The patient's wardrobe was changed, and UVA-blocking film was applied to the windows of the car and house. A decline in manifestations was seen after 18 months of improved ultraviolet protection. 