 Skin cancer is the most common cancer in Caucasians and therefore a major public health issue. Its incidence is increasing rapidly. Actinic keratosis AK is the most prevalent precancerous chronic skin condition. It can transform into squamous cell carcinoma SCC. AKs generally arise in a skin area that has diffuse precancerous damage, a phenomenon called field cancerization. Because of its precancerous character, it is advised to treat AK and herewith prevent development into SCC. The most frequently used field-directed treatments in the Netherlands are photodynamic therapy PDT, topical 5 f-fluorouracil 5 5-FU and topical 5 Imiquimod 5 IMI. Lately another topical product is approved by Dutch healthcare insurances: Ingenol mebutate IM. Up to date, which treatment the patient will receive, does not rely on evidence-based-medicine, but generally on the preference of the physician. Current national and international guidelines state no clear recommendations for the best choice of therapy. The aim of this study determine which treatment is the most effective treatment in terms of lesion reduction, costs and patient satisfaction when comparing topical treatment with photodynamic therapy PDT, 5 5-fluorouracil 5-FU cream, 5 Imiquimod IMI cream and ingenol mebutate IM gel, in treatment of actinic keratosis AK. 