An atomic-like neutral muonium center with a small anisotropy is inferred from hyperfine decoupling curves and longitudinal relaxation data on AIN. The isotropic contribution of A = 4422 M Hz, 99% of the full vacuum value, is accompanied by a weak dipolar term with D = 144 MHz as average values extracted from complete decoupling curves at a few temperatures. Simulations assuming the four nitrogen antibonding sites well reproduce the decoupling data. The hyperfine constants are consistent with those previously obtained from fitting temperature-dependent longitudinal relaxation rates to a simple model for Mu(0) motion. (c) 2005 Elsevier B.V. All rights reserved.