Sound transmission through a double wall with a masonry leaf and a lightweight leaf is examined by using statistical energy analysis (SEA). Some of the theory necessary to predict transmission is well documented and common to other forms of construction. Additional expressions are provided to account for transmission mechanisms specific to double walls. These are used in an SEA model to provide predicted data for comparison with measured results obtained from a wall tested in a transmission suite. Changes were made to the wall in order to examine the effect of placing absorbent quilt in the cavity and the effects of transmission across ties and battens bridging the cavity. The model generally gave good agreement with measured results and for each form of construction the important transmission paths were identified. These, though specific to the wall examined, do provide a general indication of the important transmission paths through this class of structure.