Abstract/Text: Q-switched lasers, with a pulse of light sufficiently short (nanosecond-domain) is demonstrated to be useful for treatment of dermal melanocytosis, blue-black tattoos, melanocytic nevi, and solar lentigines, although transient postinflammatory hyperpigmentation usually developed in the irradiated area during the following 3-4 months. If the postinflammatory pigmentation does not disappear after 1 year, incontinentia pigmenti histologica is a possibility. However, the pigment in café-au-lait macules responds variably to treatment. Melasma shows no response to laser. Therefore, accurate diagnosis is the key to success in the laser treatment. Laser treatment of vascular lesions is based on selective absorption by blood with thermal injury to the vessel wall. Therefore, the pulse-width of the vascular-specific lasers must be longer (microsecond-domain) than that of pigment-specific lasers. Because the wavelength of the lasers for vascular lesions, however, cannot penetrate into the deep areas of the skin, not all vascular lesions can be treated. Laser or light-assisted hair removal offers an efficient way to permanently reduce excessive hair growth. Skin rejuvenation is possible by laser or pulsed light with millisecond-domain pulse-width. Because these light sources, however, cause severe damage to the skin surface, the exposure energy must be reduced and the treatment must be combined with cooling devices. Therefore, the clinical results of light-assisted skin rejuvenation are not prominent. In conclusion, the pulse-width and wavelength of the laser light are critical parameters for laser treatments. If we obtain information about these parameters for specific lasers, we can expect the results of the treatment to be positive.