OUR Galaxy should contain between a hundred million and a billion neutron stars; this follows from an extrapolation of pulsar birthrates’ and from the number of supernovae required to account for the heavy-element abundances in the Milky Way(2). Only about 600 pulsars are known(3); some fraction of neutron stars will not be beaming in our direction, and therefore will not be detectable as pulsars, and some will be sufficiently old that they have stopped pulsating. How many old neutron stars exist is unknown, but based on the above numbers, about 2,000 isolated ones (not in binary systems) should he detectable as hot thermal sources, emitting X-rays as their surfaces cool or as they accrete gas from the interstellar medium(4-7). To date, however, evidence for only one has been presented(8), and its identification is ambiguous. Here we show that a bright soft-X-ray source has the properties of an isolated neutron star at a distance of about 100 parsecs. Although this confirms our present understanding of how isolated neutron stars should appear, it also highlights the significant problem of accounting for the absence of the others that should be visible.