The crystal structure of Ce1 - xLax11B6 solid solutions for various x has been studied by high-resolution powder neutron diffraction. A correction for the effect of primary extinction was applied to integrated intensities in a Rietveld program. The refinement results demonstrate good agreement with the data of X-ray single-crystal diffractometer studies performed on the same samples. Vacancies at the boron site and complete occupancy of the metal position are established for all compositions studied. The refined values of the Ce/La ratio at the metal site are in good agreement with those determined by X-ray fluorescence spectrometry on single crystals.