Let K⊂Rd be a smooth convex set and let \P_\la be a Poisson
point process on Rd of intensity \la. The convex hull of \P_\la \cap K
is a random convex polytope K_\la. As \la \to \infty, we show that the
variance of the number of k-dimensional faces of K_\la, when properly
scaled, converges to a scalar multiple of the affine surface area of K.
Similar asymptotics hold for the variance of the number of k-dimensional
faces for the convex hull of a binomial process in K