  Context. Recent metallicity determinations in young open clusters and
star-forming regions suggest that the latter may be characterized by a slightly
lower metallicity than the Sun and older clusters in the solar vicinity.
However, these results are based on small statistics and inhomogeneous
analyses. The Gaia-ESO Survey is observing and homogeneously analyzing large
samples of stars in several young clusters and star-forming regions, hence
allowing us to further investigate this issue.
  Aims. We present a new metallicity determination of the Chamaeleon I
star-forming region, based on the products distributed in the first internal
release of the Gaia-ESO Survey.
  Methods. 48 candidate members of Chamaeleon I have been observed with the
high-resolution spectrograph UVES. We use the surface gravity, lithium line
equivalent width and position in the Hertzsprung-Russell diagram to confirm the
cluster members and we use the iron abundance to derive the mean metallicity of
the region.
  Results. Out of the 48 targets, we confirm 15 high probability members.
Considering the metallicity measurements for 9 of them, we find that the iron
abundance of Chamaeleon I is slightly subsolar with a mean value
[Fe/H]=-0.08+/-0.04 dex. This result is in agreement with the metallicity
determination of other nearby star-forming regions and suggests that the
chemical pattern of the youngest stars in the solar neighborhood is indeed more
metal-poor than the Sun. We argue that this evidence may be related to the
chemical distribution of the Gould Belt that contains most of the nearby
star-forming regions and young clusters.
