  We report on an experiment that demonstrates the violation of a Leggett-Garg
inequality (LGI) with neutrons. LGIs have been proposed in order to assess how
far the predictions of quantum mechanics defy macroscopic realism. With LGIs,
correlations of measurements performed on a single system at different times
are described. The measured value of K = 1.120 +/- 0.007, obtained in a neutron
interferometric experiment, is clearly above the limit K = 1 predicted by
macro-realistic theories.
