An apparatus for processing primitives in a tile-based graphics processing system includes processing circuitry which is configured to determine, for a group of plural primitives, the rendering tiles that the group of primitives should be processed for. The processing circuitry is also configured to store, for the group of primitives, a data entry containing an indication of the identity of the plurality of primitives in the group of primitives, and an indication of the rendering tiles that it has been determined the group of primitives should be processed for.