Stereoscopic digital Particle Image Velocimetry (PIV) has been used to make a three-dimensional flow mapping of a volume of approximately 0.1 × 0.1 × 0.15 m in a laboratory model electrostatic precipitator (ESP). The mapped volume covers about two unit cells determined by the 100 mm electrode spacing in the 0.2 × 0.2 × 1.0 m ESP test section of the negative corona, barbed wire, smooth-plate kind. The barbs act as corona fix points, yielding a three-dimensional electrostatic field. The induced large-scale secondary gas velocity structures in the form of unsteadily undulating axial rolls have been analyzed for swirlnumber and location of instantaneous swirl center in 11 axial planes. The flow possesses high levels of turbulence and axial vorticity. Measured particle velocities are corrected for electrical drift to produce gas velocities. Subsequently experimental results are compared to Large Eddy Simulation (LES) results.