  This paper provides a classification result for gravitational instantons with
cubic volume growth and cyclic fundamental group at infinity. It proves that a
complete hyperk\"ahler manifold asymptotic to a circle fibration over the
Euclidean three-space is either the standard $\rl^3 \times \sph^1$ or a
multi-Taub-NUT manifold. In particular, the underlying complex manifold is
either $\cx \times \cx/\ir$ or a minimal resolution of a cyclic Kleinian
singularity.
