Let F n = (F 1,n , ...., F d,n ), n 1, be a sequence of random vectors such that, for every j = 1, ..., d, the random variable F j,n belongs to a fixed Wiener chaos of a Gaussian field. We show that, as n → ∞, the components of F n are asymptotically independent if and only if Cov(F 2 i,n , F 2 j,n ) → 0 for every i = j. Our findings are based on a novel inequality for vectors of multiple Wiener-Itô integrals, and represent a substantial refining of criteria for asymptotic independence in the sense of moments recently established by Nourdin and Rosiński [9].