The investigations of GdCa 4 O(BO 3 ) 3 single crystals grown by the Czochralski technique were performed by conventional and synchrotron radiation (SR) monochromatic wave topography mainly in back reflection geometry. It was found that back reflection topography is effectively able to reveal the dislocation structure even in thin samples. Different distribution of defects was observed in samples cut off from the top, middle and end part of the ''as-grown'' crystal. SR monochromatic wave topographs taken for two flanks of the rocking curve show the characteristic inversion of diffraction contrast. Both monochromatic wave and projection Lang topographs did not reveal any segregation fringes proving high homogeneity of the chemical composition of the examined crystal.