Skin disorders such as, for example, atopic dermatitis, dyshidrosis, eczema, lichen planus, psoriasis, and vitiligo, are treated by applying high doses of ultraviolet light to diseased regions of a patient's skin. The dosage exceeds 1 MED as determined for the particular patient and may range from about 1 MED to about 20 MED or higher. The ultraviolet light has a wavelength within the range of about 295 nanometers to about 320 nanometers. High doses of ultraviolet light are preferably restricted to diseased tissue areas. A specialized handpiece provides a beam profile especially suitable for application of controlled doses. A specialized delivery device is useful for UV treatment of tissue within the mouth.