A quantitative study of the axial and tangential components of the mean velocity in a 3″-hydrocyclone using laser doppler anemometry has revealed multiple reverse flows in the vortex core. Flow visualization by dye injection shows that these flows are coherent over a significant portion of the hydrocyclone and that little radial mixing occurs between these secondary flows and the outer helical flow. A 2:1 contraction in the vortex finder plays an important role in causing four distinct simultaneous countercurrent flows in the conical section of the hydrocyclone.