An optical fibre sensor for short pulse duration x-ray dosimetry is presented. The sensor is based on luminescence generated in the cladding of a 1 mm core diameter polymer optical fibre which has been doped with a radioluminescent phosphor. On interaction with x-rays, this phosphor emits visible light, part of which is coupled to the fibre core through a combination of surface roughness at the core¿cladding interface and through evanescent wave coupling of these guided waves. From here it is transmitted to an optoelectronic photodetector for monitoring. A 15 cm fibre sensor was used for the experiment which was conducted using a pulsed x-ray source normally employed for the preionization of excimer lasers. The results are calibrated against the emission intensity from a scintillating plastic block and a pen dosimeter. The peak output signal of the fibre sensor increases linearly with the dose produced by the x-ray source. There is also a discussion on the long-term stability of such a sensor, the expansion of this sensor into a multi-point device and methods to improve the efficiency of the luminescence coupling from cladding to core for large core polymer fibres included.