An anionically polymerized impact-modified polystyrene has a yield stress of at least 24 MPa, measured at 23.degree. C. to DIN 53455 and a hole impact strength of at least 11 kJ/m.sup.2, measured at 23.degree. C. to DIN 53753, measured in each case on a specimen produced to ISO 3167. A preparation process is described.