In the tunnel model, a fluid is regarded as being composed of rows of molecules, which move almost in one dimension along lines or tunnels, the walls of which are formed by neighboring rows of molecules. This model provides a simple and reliable theory for a classical system of dense hard spheres. The tunnel model has also been applied to quantum hard spheres. However, until recently, there have been no reliable results for dense quantum hard spheres, so that the accuracy of the quantum tunnel model could not be judged. Comparison with a recent variational determination of the ground-state energy of a system of hard spheres shows that the tunnel model is reliable for this system.