In an experiment conducted at the Tomsk synchrotron "Sirius", the photon yield of parametric X-ray radiation generated by 500 MeV electrons in a tungsten monocrystal in Bragg geometry has been studied. The (111) tungsten monocrystal, having a thickness of 1.7 mm and a surface mosaicity of not more than 80², was oriented at the Bragg angle θB= 45°to the direction of the electron beam. The photons were detected at the angle 2θB= 90° relative to the electron beam. A comparison of PXR angular distributions with calculations has been carried out with taking into account the actual conditions of the experiment.