The structure and compressibility of synthetic lanthanide-doped zircon (ZrSiO4 with a total of 2.0 mol% trivalent Gd, Dy, Er, Yb, and Y, charge-balanced by addition of P5+) were determined from static compression experiments to 25.9 GPa. The sample bulk modulus, K-T0 = 189± 1 GPa is 5% lower than K-T0 for undoped zircon, and the sample transforms from the zircon to the scheelite structure above 22.6 GPa, 3 GPa greater than the transformation pressure in pure ZrSiO4. A simple model is presented linking compressibility with unit-cell volume for zircon-structured and scheelite-structured ABO(4) compounds, allowing prediction of the compressibility of zircon-structured vanadates and phosphates.