We revisit the density profile of the galaxies cluster MS 2137-23 by modelling strong lensing, weak lensing data and the velocity dispersion profile of the central cD galaxy. Though we are able to model the lensing properties with a NFW density profile, this latter model cannot explain well the velocity dispersion nor the X-rays properties. To accommodate all these independent constraints, one needs to go beyond the over-simplistic assumption of spherical symmetry. The higher mass and concentration inferred from lensing suggests that the dark matter halo is elongated along the line of sight. The misalignment between the projected dark matter and stellar components also supports this scenario. Neglecting projection effects leads to systematic discrepancies between mass estimates. We thus argue that a fully triaxial modelling of haloes is a major concern for precision mass estimates.