Experimental results and initial clinical experience indicates that even carcinoma in situ can be destroyed by integral photodynamic therapy of multifocal bladder carcinoma following tumor-selective photosensitization with a hematoporphyrin derivative. The employment of a light-scattering medium in combination with a special bladder catheter and photodynamically effective red laser light (630 nm) guarantees homogeneous irradiation of the bladder, which thus reaches all tumor foci. The complications observed were transitional dysurias and, in a particular case, regressive shrinkage of the bladder.