Knowledge of interference effects are of the utmost importance to the reliable design of satellite communication systems. In this paper interference caused by differential rain attenuation from an adjacent Earth-space system operating at the same frequency is considered as dominant. In particular, a method to predict rain differential attenuation statistics used for single-site Earth-space systems is extended to include dual-site diversity systems. Just as with the original method the modified one is again based on a model of convective rain cells and on the lognormal model for point rainfall rate statistics. The effects of various parameters on the diversity gain, corresponding to the carrier-to-interference ratio, are calculated numerically, leading to some very useful conclusions. ¿ American Geophysical Union 1996