Abstract: The invention provides a fluorescence illumination adapter capable of being fitted to a wide range of existing stereomicroscopes. The fluorescence illumination adapter attaches to the stereomicroscope barrel that contains the imaging optics, and has high intensity light-emitting diodes that stimulate fluorescence in a specimen. A removable barrier filter is positioned in the optical path underneath the stereomicroscope barrel to prevent the fluorescence stimulating light entering the imaging optics. The light-emitting diodes are mounted on pivoting elements so that the location of the illumination spot on the specimen can be easily adjusted. The adapter also incorporates a white light-emitting diode source that can be used either for white-light viewing or for selective mixing with the fluorescence excitation illumination. The barrier filter is easily removed to facilitate rapid switching between fluorescence and white-light viewing.