The effect of surface tension on extrudate swell of a Newtonian fluid from square and rectangular channels is presented. Surface tension decreases extrudate cross sections in all cases examined. The influence on the shapes of final extrudate profiles is found to be greater for channels with higher aspect ratios. Surface tension has the greatest influence on the swell of the longer side of the extrudate while that of the shorter side is virtually unaffected. The effect of the capillary number can be significant and in certain cases should be considered in the design of extrusion dies.