The spin wave dispersion relation in both clean and disordered itinerant quantum ferromagnets is calculated. It is found that effects akin to weak-localization physics cause the frequency of the spin-waves to be a nonanalytic function of the magnetization m. For low frequencies Ω, small wavevectors k, and small m, the dispersion relation is found to be of the form Ω m^1-α k^2, with α = (4-d)/2 (2<d<4) for disordered systems, and α = (3-d) (1<d<3) for clean ones. In d=4 (disordered) and d=3

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... n), Ω m ln(1/m) k^2. Experiments to test these predictions are proposed.