The influence of the feed opening axis width and position in relation to the plasticizing system axis on the effectiveness of the extrusion process of poly(vinyl) chloride has been studied. The research was conducted on the extrusion line for profiles with the extruder of the screw diameter 25 mm and L/D ratio = 25. In the extruder, the extruder head was mounted with a die of a rectangular cross-section shape for extruding a sheet of a defined width and thickness. The extruder was adapted for mounting five feed segments in the feed zone of the plasticizing unit; the segments differed from one another in terms of their feed opening width, the values of which were 0.6 D, 0.7 D, 0.8 D, 0.9 D and 1.0 D, respectively, whereas the values of the longitudinal axis shift of the opening relative to the longitudinal axis of the plasticizing unit were 0.2 D, 0.15 D, 0.10 D, 0.05 D and 0.0 D, respectively, which corresponded to 5 mm, 3.75 mm, 2.5 mm, 1.25 mm and 0 mm, respectively. The effectiveness of the polyvinyl chloride extrusion process was determined by dependences of extrudate temperature, extruder screw torque, polymer mass flow rate, power supplied to the extruder and conveyed by the polymer, unit energy consumption and energy efficiency of the extrusion process on the feed opening width and its axis position relative to the plasticizing unit axis, at different values of the screw rotational speed. It was stated that the width and position of the feed opening in relation to the plasticizing system axis can be adjusted in such a way that the extrusion process will be the most effective and other conclusions were also drawn.