The combined influence of stress concentration, weld line, and local distribution of molecular orientation on injection molded polystyrene (PS) plates with a molded-in hole is described. Birefringence measurements were used to investigate the molecular orientation, and three-point flexure was used to investigate the mechanical properties. Both blunt notch tests and transverse bending tests were carried out. Blunt notch tests showed a strong variation of the material resistance to fracture around the hole. The molecular orientation increased the material resistance not only at the hole equator, but also at the flow split area. In a large domain, weld line fracture was the dominant fracture mechanism. Transverse bending tests also showed a strong influence of the molecular orientation on the load-carrying ability. The weld line was definitely the weakest region, but the reduction caused by the weld line itself appeared to be small.