We read with great interest the article Gentry et al. (1) which explores the impact of expanding kidney paired donation (KPD) through participation by compatible pairs. In their abstract they argue that this is a new paradigm of KPD and in their conclusion they indicate that the inclusion of recipients with compatible donors will greatly increase the number of incompatible pairs matched through KPD. While we strongly support this conclusion, they neglected to mention that the impact of expanding KPD through participation by compatible pairs had been examined earlier (2,3). Roth et al. (3) uses a similar technique of optimization due to Edmonds (4) as used in Gentry et al. (1), although the two papers differ in the construction of the simulated donor-recipient pairs in the KPD pool. For simplicity of the simulations, all pairs were assumed to be nonblood-related in Roth et al. (3), while Gentry et al. (1) include blood-related pairs. Roth et al. (3) also concluded that the largest gains to incompatible pairs in KPD will come from the inclusion of compatible pairs to KPD. Based on results from (2,3), the three authors of this letter collaborated with the first two authors of Gentry et al. (1) to produce a consensus kidney paired donation matching statement which includes participation of compatible pairs in KPD as a parameter to be considered in designing a national KPD matching program (5). A. E. Rotha, T. Sönmezb and M. U. Ünverc aHarvard Business School and Department of Economics, Harvard University, Cambridge, MA bBoston College, Department of Economics, Chestnut Hill, MA cUniversity of Pittsburgh, Department of Economics, Pittsburgh, PA