We studied the influence of the lattice structure on the chromium magnetism in Ag/Cr multilayers by combining structural characterization techniques and perturbed angular correlation spectroscopy. Chromium in Ag/Cr multilayers orders as an incommensurate longitudinal spin-density wave (SDW) with the spins oriented out of plane. A size effect induces the instability of the SDW below a critical chromium thickness. The absence of the spin-flip transition, the position of the Neel temperature, and the actual character of the SDW are attributed to the specific structural properties. [S0031-9007(98)07171-3].