beta Pictoris is the best known example of a main-sequence star encircled by a tenuous disk(1), Optical(2,3) and infrared(4) images of beta Pic suggest that the disk is composed of dust grains which have been interpreted(1) as the debris generated by the disruption of the asteroid-sized remnants of planet-formation processes(5), The star itself is relatively old, with an age in excess of 100 Myr, Here we present high-resolution millimetre-wave images of continuum and molecular-line emission from dust and gas surrounding a much younger star, MWC480 : the stellar properties of MWC480 are similar to those of beta Pic, but its age is just 6 Myr, The morphology of the circumstellar material and a comparison with the predictions of kinematic modelling indicate the presence of a rotating disk, gravitationally bound to the star, Moreover, the mass of the disk is greater than the minimum required to form a planetary system like our own(5), We therefore suggest that the disk around the young star MWC480 could be a progenitor of debris disks of the type associated with older stars such as beta Pic, and so holds much promise for the study of both the origin of debris disks and the early stages of the formation of planetary systems.