The fracture behaviour of thermoplastic poly(ethylene terephthalate) reinforced with short E-glass fibre was investigated using fractography and a fracture mechanics approach. The observed microstructures, crack propagation and the stress-rupture lifetime data indicate a sudden breakdown induced by far-field effectS. The critical damage appears to be correlated with a ductile-to-brittle transition of matrix fracture. The calculation of fracture toughness for various fibre orientations indicates that the fibre pull-out energy is the dominant term in the case in which the fibre orientation is perpendicular to the notch tip.