Photodynamic therapy (PDT) with topical aminolevulinic acid (ALA) is currently approved in the US and Canada for the spot treatment of non-hypertrophic actinic keratoses of the face and scalp. Dermatologists are currently using ALA-PDT on larger skin surfaces for the treatment of extensive actinic keratoses, sun damage P and acne. This article reviews the safety and efficacy of large surface ALA-PDT for the treatment of actinic keratoses and photodamage. New data on the carcinogenic potential of weekly topical ALA-PDT in mice is also presented. Groups of hairless mice were treated weekly with either ALA alone, blue light alone or ALA-PDT using blue light for a total of 10 months followed by an additional 2 months or observation. Mice were examined weekly for the presence of skin tumors. Skin tumors were not observed in mice treated weekly with blue light alone, with topical application of ALA alone or with ALA-PDT.