Essential work of fracture methodology was used to determine plane-stress ductile fracture toughness of high impact polystyrene film of thickness 0.26 mm. Results obtained indicated that specific essential work of fracture, w(e), is independent of loading rate, and for certain specimen sizes, independent of both gauge length and width of the specimen. On the other hand, w(e) was found to be affected by the temperature, molecular anisotropy and the geometry of the test specimens. Reasonable estimate of w(e) was obtained via crack opening displacement value. (C) 2003 Kluwer Academic Publishers.