KGe2(PO4)(3) has been prepared in both crystalline and vitreous forms. The NZP-type structure of the crystalline variety and its thermal expansion have been investigated by X-ray powder diffraction. The crystal structure has been refined by the Rietveld method in the space group R (3) over bar. The thermal expansion coefficients have been determined between room temperature and 600 degrees C and compared to dilatometry measurements. The parameters a and c have a positive and isotropic behavior and the average macroscopic thermal expansion coefficient, , is 10 x 10(-6) degrees C-1 at 600 degrees C. A comparison with the thermal expansion of the related Li and Na compounds is reported.