The results are reported of an extensive experimental investigation of turbulent flow of polymeric non-Newtonian liquids (0.01, 0.075, 0.125 and 0.175% polyacrylamide (PAA) solutions) through a plane sudden expansion of expansion ratio R = 1.43 and aspect ratio A = 13.3. Three water-flows are also reported for comparative purposes. A laser Doppler anemometer was used to measure mean and RMS streamwise velocities, U and u', as well as the transverse mean and RMS velocities, V and v', and the Reynolds shear stress (uv) over bar. For the water-flows we highlight the important influence on the reattachment length of the maximum turbulence intensity at separation. The PAA flows exhibit an increased reattachment length compared with the Newtonian situation. The magnitudes of the recirculating velocities and recirculating flowrates are increased for the lowest concentration (0.01% PAA) but decreased for the more viscoelastic high concentration (0.075-0.175% PAA) flows. In all cases these changes are accompanied by large reductions in the transverse turbulent intensity. The correspondingly high degree of turbulence anisotropy is instrumental in generating increased reattachment lengths for the lower concentration flows. The increased levels of viscoelasticity for the higher concentration PAA solutions lead to a reduction of the turbulence intensity at separation and this effect, coupled with the high turbulence anisotropy, plays an important role in increasing the reattachment length.