In the PDT group the patients will apply a chemical sunscreen (SPF 50+) to the whole face and other light-exposed, unprotected areas of the skin. After at least 15 minutes a lesion preparation of AKs (removal of crusts) will be performed and MAL will be applied in a thin layer to the whole face. Within 30 min after MAL application patients expose themselves to daylight for 2 hours. In the control group, cryosurgery will be performed using liquid nitrogen spray in each AK lesion; this will be done at visit 1 and, if necessary, also at visits 2-5. At visits 2-6, the efficacy of the treatment will be evaluated by the observer by documenting all existing and newly appearing AKs in the face.