The fracture behavior of sheets of rigid poly(vinyl chloride), PVC, 2 to 10 nun thick, was investigated according to the Essential Work of Fracture (EWF) approach in order to find evidence of thickness effects, Test pieces were doubly notched and loaded in tension. Critical values of the J-integral were measured, in three-point bending, either complying with or violating the size requirements dictated by the ASTM 813.89 protocol, It was found that J(c) did not depend on sample thickness; on the contrary, the value of the Specific Essential Work of Fracture, obtained by means of test pieces with ligaments larger than three times the thickness, was strongly affected by the sample thickness. The size of the plastic zone that developed around the ligaments was measured by optical means, At small ligaments the height of this zone linearly increased with ligament size and tended to level off at large ligaments. In the linear range, the rate of increase of the size of the plastic zone did not depend on sample thickness. It was found that the value of the Specific Essential Work of Fracture obtained by test pieces whose plastic zones were in the linear range was independent of thickness.