Cosmological perturbations of quantum mechanical origin: Are nonvacuum initial states allowed?

We address the question of whether nonvacuum initial states for cosmologica l perturbations are allowed, or whether they are ruled out on the basis of present experimental and observational data. Our choice of a nonvacuum init ial state is guided by the idea that the initial state could have a built-i n characteristic scale. We Find that a class of initial states can fit the data; however, the initial states must be close to the vacuum.