The present invention provides methods and systems for performing in-vivo flow cytometry to obtain desired information regarding one or more cell types of interest flowing through a subject's circulatory system. In one embodiment of the invention, a portion of the subject's circulating blood is illuminated with radiation having multiple wavelength components, and the backscattered radiation generated in response to the excitation radiation is detected at a plurality of scattering angles and analyzed to derive the desired information.
