Stereoscopic Particle Image Velocimetry (S-PIV) measurements are performed to analyse the flow field in a sudden expansion with an expansion ratio of 4.9:1. The velocity profile in the inlet tube is measured using Laser Doppler Anemometry (LDA) and the Reynolds number (Re) is varied from 3150 till 63300. The time-averaged flow field is found to be axisymmetric and has a jet-like velocity profile near the nozzle with a spreading rate comparable to free round jets. Despite the axisymmetric nature of the mean flow field, it contains unsteady coherent structures, which are analysed using both Spectral Proper Orthogonal Decomposition (SPOD) and phase averaging. It is found that the instantaneous flow field is asymmetric and it precesses around the central axis of the geometry. The structure of this precession is similar for all Reynolds numbers investigated and the Strouhal number increases with increasing Reynolds number till Re =26000, after which it reaches a constant value of around 3 × 10 −3 . These precessing structures were previously only reported for swirling sudden expansion flows or flows in dedicated free jet nozzles, but this study shows they also exist in confined nonswirling sudden expansion flows.