Intravenously administered hematoporphyrin derivative photosensitizes tumorous bladder tissue which can then be destroyed selectively by irradiation with red laser light (630 nm). After experimentally developing a concept since 1978 (light diffusion medium, special bladder catheter) to expose the bladder to the therapeutically effective red laser light, the integral photodynamic therapy is meanwhile performed clinically. The experience gained so far demonstrates that especially the multifocal carcinoma in situ up till now difficult to be detected endoscopically represents a new domain for the integral photodynamic therapy.