We compute the high-temperature limit of the free energy for four-dimension
al N = 4 supersymmetric SU(N-c) Yang-Mills theory. At weak coupling we do s
o for a general ultrastatic background spacetime, and in the presence of sl
owly-varying background gauge fields. Using Maldacena's conjectured duality
, we calculate the strong-coupling large-N-c expression for the special cas
e that the three-space has constant curvature. We compare the two results p
aying particular attention to curvature corrections to the leading order ex
pressions.