Dermatologic radiotherapy is based on the standard physical and radiobiological parameters. The radiation quality most often used in dermatology lies between 10 and 50 kV. Another important parameter is the half-value depth which should correspond to the depth of the tumor below the skin surface. In this way the skin is not over-exposed to radiation treatment. Indications for radiotherapy of malignant skin tumors include basal cell carcinoma, squamous cell carcinoma, severe actinic keratoses, lentigo maligna, lentigo maligna melanoma, Merkel cell carcinoma, and Kaposi sarcoma, as well as T- and B-cell lymphomas. Most patients with malignant skin tumors require life-long monitoring after radiotherapy. The most common benign lesions where radiotherapy may be indicated are eczemas, psoriasis, and keloids, but its use should be carefully weighed in these settings.