A non-Boltzmann sampling method is demonstrated for efficient calculation of structural properties of models having ab initio interaction potentials. A sample of independent configurations is generated with a molecular dynamics simulation using an approximate potential. Ab initio calculations, done only at the sampled configurations, are used to correct the thermal averages of any mechanical variable for the difference between the approximate and ab initio potentials. Tests of the method show that relatively few ab initio calculations are needed to obtain significant structural information and that bootstrap estimates of the uncertainties are reasonable. As a further test, we use results from a previous calculation of the hydration free energy of Na+ at 973 K and 0.535 g/cm(3) to calculate the Na-O pair correlation function and coordination number for an ab initio model of Na-H2O interactions.