Background Actinic keratoses (AKs) are often treated separately, lesion by lesion. However, in the past years, AKs have been described as a field disease and not limited to single clinically apparent lesions. Treatment should therefore target an area of field change which may treat the subclinical AKs and reduce the risk of development of further AKs, second tumours, and local recurrence. Objectives The investigators sought to investigate whether field ALA-PDT of facial actinic keratosis would prevent new AKs, in comparison with a lesion area receiving the same ALA-PDT, in patients with clinical signs of field cancerization. Methods Eighty patients, previously diagnosed as having AKs of the face, were randomized distribution into two groups. 10% aminolaevulinic acid (ALA)-PDT for field treatment was on one group and for a lesion area (Vehicle control cream was applied to the non-lesion area) was on the other group. During the next 5-year period of follow up, patients were clinically evaluated for new AKs.