Abstract. We prove that the dimension of any asymptotic cone over a metric space (X, ρ) does not exceed the asymptotic Assouad-Nagata dimension asdim AN (X) of X. This improves a result of Dranishnikov and Smith (2007), who showed dim(Y ) ≤ asdim AN (X) for all separable subsets Y of special asymptotic cones Cone ω (X), where ω is an exponential ultrafilter on natural numbers.We also show that the Assouad-Nagata dimension of the discrete Heisenberg group equals its asymptotic dimension.