Several very extended (0.5-1 micros) molecular dynamics (MD) simulations of parallel and antiparallel G-quadruplex DNA strongly suggest that in the presence of suitable cations the quadruplex not only remains stable in the gas phase, but also displays a structure that closely resembles that found in extended (25-ns long) trajectories in aqueous solution. In the absence of the crucial cations, the trajectories become unstable and in general the quadruplex structure is lost. To our knowledge, this is the first physiologically relevant structure of DNA for which very large MD simulations suggest that the structure in water and in the gas phase are indistinguishable.