The fatigue crack growth resistance of a Tibeta21s/SCS-6 composite at room temperature has been characterised experimentally and analysed theoretically. Particular attention has been paid to the transition from crack-arrest (CA) to catastrophic specimen failure (CF), and emphasis has been placed on the influence of the extrinsic factors of initial notch length, specimen width and loading configuration, and of the intrinsic fibre strength distribution on this transition. Experimental results show a marked influence of extrinsic factors on the CA/CF transition, and they also reveal the importance of fibre strength on the fatigue crack growth resistance of the composite. The stress in bridging fibres has been analysed theoretically, and the results have been used to explain the experimental observations. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.