In this paper, the performance of a closed circuit HPGR. operation was evaluated by the data obtained from six measurements in a cement grinding circuit operating in Turkey Flowrates of the streams and classifier performance were evaluated after mass balancing. The average specific energy consumption of the HPGR for six measurements was 9.62 kWh/t for grinding from 17.9 mm to 57 mu m (80 % passing size). Reduction ratio increased with the increase in specific energy consumption. Although cut point and the bypass of the classifier varied in a rather wide range, reduced efficiency curve and imperfection values indicated that the sharpness of separation remained the same.