A phototherapeutical apparatus and method are described. The apparatus includes an ultraviolet light source, an optical guidance system, and a patient interface. The patient interface is insertable at least partially into a body cavity and is operable to apply the guided ultraviolet light to a tissue surface of a body cavity. The method includes providing the phototherapeutical apparatus, preparing for the application of the phototherapeutical apparatus, inserting the patient interface at least partially into a body cavity, and applying the ultraviolet light by the patient interface to a tissue surface of a body cavity, wherein the tissue of the body cavity has an inflammatory or a hyperproliferative disease. The inflammatory diseases include rhinitis, sinusitis and rhinosinusitis. A photochemotherapeutical method is also described, using photosensitizing substances, such as psoralen before treatment with ultraviolet light. The phototherapeutical method is also effective for the prevention of inflammatory or hyperproliferative diseases.