Photodynamic therapy (PDT) consists of topical or systemic delivery of photosensitizing drugs followed by irradiation with light. Topical PDT is currently carried out with 5-aminolaevulinic acid (ALA) or methylaminolaevulinate (MAL) both metabolized in the cells to protoporphyrinIX (PpIX), a photosensitizing molecule absorbing visible light. As the rate of ALA-induced PpIX synthesis and accumulation is higher in malignant cells than in normal ones, PDT is able to exert a selective action on neoplastic tissues. PpIX transfers its energy to molecular oxygen generating reactive oxygen species. The subsequent oxidation of lipids, amino acids and proteins together with transcription and release of inflammatory mediators induces cell necrosis, apoptosis and immunemodulation. ALA 20% or MAL 16% (solution or cream) are applied over the skin lesion and then irradiated with blue or red light, depending on the thickness of the tumour. No anaesthesia is needed. Usually two-three treatments are sufficient for actinic keratosis, basal cell carcinoma, Bowens disease, the main dermatologic indications for PDT. Topical PDT is well suited for lesions that would otherwise require extensive surgical procedures and for patients with contraindications to surgery or with multiple lesions. We review action mechanism, procedures and indications of PDT for non-melanoma skin cancers.