Background: Porphyrin metabolism disorders, known as porphyria, represent inherited or acquired diseases. The development of porphyria due to light sensibility occurs especially with exposure to wavelengths in the range of 300-700 nm. Skin reactions and neurovisceral dysfunctions are known side effects of ionizing irradiation. It can be postulated that during or after ionizing irradiation treatment of patients affected with tumor and porphyria, severe side effects might appear, in contrast to patients without porphyria. This paper describes the treatment of 2 patients affected with tumor and concomitant porphyria. Patients: One female patient suffering from intermittent porphyria and breast cancer and one male patient suffering from porphyria cutanea tarda and bladder cancer were treated with ionizing irradiation (electrons and photons). No abnormalities nor any severe general or local side effects could be observed. Conclusion: Radiation therapy is not a `stimulating' factor in activating porphyria symptoms.