Dye lasers are useful for treating pigmented skin lesions, but their equipment is expensive and bulky. A simple and cheap phototherapy would be acceptable to dermatologists for treating pigmented skin lesions such as nevus of Ota. We investigated as a pilot study whether dermal injection of riboflavin and exposure to near-ultraviolet/visible radiation (ribophototherapy) decreases the dermal pigment of blue nevi which are recalcitrant to laser therapy. The therapeutic efficacy was assessed by comparison of the amount of dermal pigment in hematoxylin-eosin specimens taken before and after treatment. Pigmentation of the nevus became faint to the depth of 1 mm with little noticeable epidermal change after 21 treatments. At the deeper dermis somewhere between 3 and 4 mm from the epidermis, ballooning degeneration of the dermal cells was observed in hematoxylin-eosin specimens. Ribophototherapy is hopeful for treating pigmented skin lesions.