Weight optimization of a sandwich panel was performed. The constraints were both mechanical, in the form of stiffness and strength constraints, and acoustic, in the form of a required sound reduction index, R. The sound reduction index of the optimized panel and an initial configuration was measured under laboratory conditions and the results were compared to predicted values. Predictions and measurements of the sound reduction index were made in third-octave frequency bands. It was shown that the difference in R between the initial panel and the optimized one was predictable using the acoustic models and that the optimized panel fulfilled the constraints. The weighted average reduction index, R-W, was also used to provide an engineering number for comparison.