In this paper we present and demonstrate a technique for mapping fluid flow rates in microfluidic systems with sub-micron resolution using confocal microscopy in conjunction with fluorescence correlation spectroscopy. Velocity profiles and velocity images of the fluid within poly(dimethylsiloxane)-glass microchannels are presented and analyzed. Flow velocities ranging from a few µm/s to a few cm/s can be recorded using nanometer-scale fluorescent polymer spheres as fluid motion tracers. The method is applied to mapping the hydrodynamic flow velocity in complex geometries. This is, to our knowledge, the first report of FCS for producing 2-dimensional velocity maps.