Performance and laser measurement results are presented for a transonic centrifugal compressor stage, equipped with a backswept rotor designed for 586 m/s tip speed and a mean relative inlet tip Mach number of 1.30. The flow field features of the rotor are analysed in detail with the help of laser measurements and the results obtained from a 3D viscous calculation. Both laser measurements and calculations are carried out for the impeller’s design point and a comparison between measured and calculated data is presented for four measurement planes representing the inlet, exit and channel flow conditions. The maximum relative Mach number is found to be 1.45 and a jet/wake type flow exists in the rear part of the flow channel with the wake concentrating in the shroud region. For the operating point investigated, the wake development is due more to the strong shroud curvature in the meridional plane than to a shock induced boundary layer separation. Laser measurements and calculations point to a significant flow displacement in the impeller exit region caused by the wake flow. The theoretical results indicate that a flow separation occurs also at the front side of the vaneless diffuser.