Recent discoveries of objects orbiting beyond Neptune(1-5) have emphasized that our understanding of the distribution and dynamics of material in the outer Solar System is very incomplete. This trans-neptunian population-known as the Kuiper belt-is thought to act as a relatively stable reservoir of objects that could become short-period comets(6-9), although there may be other regions of stability in the outer Solar System that could also supply such comets. Here I use numerical simulations to identify one such long-lived region between the orbits of Uranus and Neptune. I show that in the region 24-27 AU from the Sun, about 0.3 per cent of an initial population of small bodies moving on low-eccentricity, low-inclination orbits could survive for the age of the Solar System. The actual existence of this hypothetical belt is not precluded by currently available observational Limits, and there could be as much as similar to 5 x 10(-4) Earth masses of material populating this region-comparable to the mass of the asteroid belt between Mars and Jupiter.