We have performed NMR spin-lattice relaxation experiments and molecular dynamics (MD) computer simulations on atactic polystyrene (a-PS). The segmental correlation times of three different molecular weight a-PS (M-n = 1600, 2100, 10 900 g/mol) were extracted from NMR by measuring the H-2 spin-lattice relaxation times (T-1) over a broad temperature range (390-510 K). MD simulations of an a-PS melt of molecular weight 2200 g/mol were carried out at 475, 500, and 535 K. Comparisons between experiments and simulations show that the MD simulations reproduce both the shape of the P-2(t) orientation autocorrelation function and its temperature dependence, while the simulated segmental correlation times are slower than experimental results by a factor of 1.8. If the simulations are resealed by this factor, they reproduce both the experimental T-1 values and the slight difference in dynamics between the backbone and side group of PS.