The hydrodynamics generated by a rotor-stator mixer has been characterized experimentally in terms of power draw and flow patterns with viscous Newtonian and shear-thinning fluids. The power consumption was correlated to the impeller speed and represented by means of the dimensionless power number versus Reynolds number curve. The impeller shear rate constant, determined from a macroscopic balance as well as with the Metzner-Otto method, was found to be dependent on the fluid theological properties. An attempt was also made to determine the pseudo-cavern (well-mixed region surrounded by a stagnant fluid) dimension as a function of the hydrodynamic parameters. Results show that the shape and magnitude of the pseudo-caverns in the vicinity of the rotor-stator mixer are central to the understanding of the relationship between the power draw and the ability of the impeller to mix the fluid into the vessel.