  We discuss the quasi-normal modes of massive scalar perturbations of black
holes in AdS_5 in conjunction with the AdS/CFT correspondence. On the gravity
side, we solve the wave equation and obtain an expression for the asymptotic
form of quasi-normal frequencies. We then show that these expressions agree
with those obtained from a CFT defined on $\mathbb{R} \times S^3$ in a certain
scaling limit, by identifying Euclidean time with one of the periodic
coordinates. This generalizes known exact results in three dimensions (BTZ
black hole). As a by-product, we derive the standard energy quantization
condition in AdS by a simple monodromy argument in complexified AdS space. This
argument relies on an unphysical singularity.
