  We report on high resolution Echelle spectroscopy of 20 giant stars in the
Galactic old open clusters NGC 6791 obtained with Hydra at the WIYN telescope.
High precision radial velocity allow us to isolate 15 {\it bona fide} cluster
members. From 10 of them we derive a global [M/H]=+0.39$\pm$0.05. We therefore
confirm that NGC 6791 is extremely metal rich, exhibits a few marginally
sub-solar abundance ratios, and within the resolution of our spectra does not
show evidences of spread in metal abundance. With these new data we re-derive
the cluster fundamental parameters suggesting that it is about 8 Gyr old and
4.3 kpc far from the Sun. The combination of its chemical properties, age,
position, and Galactic orbit hardly makes NGC 6791 a genuine Population I open
cluster. We discuss possible interpretations of the cluster peculiarities
suggesting that the cluster might be what remains of a much larger system,
whose initial potential well could have been sufficient to produce high
metallicity stars, and which has been depopulated by the tidal field of the
Galaxy. Alternatively, its current properties may be explained by the
perturbation of the Galactic bar on an object originated well inside the solar
ring, where the metal enrichment had been very fast.
