Background: Photodynamic therapy(PDT) is a type of photochemotherapy that is designed to kill targeted tumor cells. Objective : The Clinical effects of PDT were analysed for response rates, post-treatment healing and adverse effects on several cutaneous carcinoma in situ. Method: PDT with topical 5-aminolevulinic acid-based irradiation of corresponding 630+5nm light was performed in 6 carcinoma in situ patients who had actinic keratosis, Bowen' disease or cutaneous squamous cell carcinoma. Result: In all patients the clinical results were exellent with respect to initial complete responses and cosmetic outcome. Conclusion :PDT might be chosen as a first line treament for cutaneous carcimoma in situ. (Korean J Dermatol 1998;36(3): 407-414)