Photodynamic therapy is a treatment modality that has been shown to be effective mainly for the dermato-oncologic conditions: actinic keratosis, Bowen's disease, in situ squamous cell carcinoma and basal cell carcinoma. Recent work has focused on the development and evaluation of topical photosensitizers like the haem precursor 5-aminolevulinic acid or its methyl ester, both inducing photosensitizing porphyrins. These drugs do not induce strong generalized cutaneous photosensitization, unlike the systemically applied porphyrins or their derivatives. For dermatological purposes incoherent lamps or light-emitting diode arrays can be used for light activation. Cure rates reported for very superficial lesions (tumour thickness <2-3 mm) are comparable to those achieved by other therapeutic modalities. Photodynamic therapy is a minimally invasive therapy associated with excellent cosmetic results. For actinic keratosis and basal cell carcinoma, methyl aminolevulinate-photodynamic therapy is already approved in Europe, Australia and New Zealand, and is now also approved for actinic keratosis in the US.