A diagnosis device having an illumination system configured to produce white light along an illumination path, an observation system for observing the target region in a white-light and fluorescence mode, the observation system having an observation path having at least one first image sensor for receiving a white-light image and at least one second image sensor for receiving a fluorescence image, an observation spectral filter in the observation path are configured such that light in the spectral range of the fluorescence can be fed to the second image sensor while light in the spectral ranges outside of the fluorescence is blocked. An illumination spectral filter is arranged in the illumination path and having a characteristic of the observation spectral filter such that the target region is illuminated with the whole spectral range of the white light with the exception of the spectral range of the fluorescence to be observed.