The evolution of a central longitudinal defect was investigated for an austenitic stainless steel of type AISI 304L by preparing 12.5 mm round bars with a 4 mm round hole of length 100 mm. The evolution was monitored by taking out bars, rolled 1, 1+2, 1+2+3 passes and so on, from a wire rod block operated at a final exiting speed of 60 m/s. Cross sections of the rolled bars through the central defect were investigated with respect to geometrical changes and microstructure. The rolling process of the first 4 passes were analysed with FEM. The results show good agreement between simulations and experiments. In general, the defect is reduced quicker in size than predicted by a pure geometrical scaling. The analyses show that the round passes are more effective in reducing the defect size than the ovals. The velocity changes imposed by the central defect closing and reopening is analysed.