Recently, Holowinsky and Soundararajan have proven that the L^2 mass of a sequence of holomorphic Hecke eigenforms of large weight on SL(2,Z) becomes equidistributed, settling a case of the quantum unique ergodicity conjecture of Rudnick and Sarnak. I will present a generalization of their work to holomorphic forms on noncompact Hilbert modular varieties over any totally real field, or more generally, automorphic forms of cohomological type on GL(2) over any number field.  I will also give an application of the result in the holomorphic case to the equidistribution of zero divisors of modular forms.