Data reported in this work are the result of the first crystallomorphological analysis of the formation of most typical structural defects in growing large BBO crystals by the top seeded solution growth (TSSG) technique combined with pulling. These defects are grain boundaries with varying scales of disordered angle orientations and melt inclusions. It is these defects that to a great degree restrict the yield of suitable material of high-optical quality from grown BBO boules. We believe that the main reason for the formation of these defects is the incoherent joining of different sectors of independent growth, which form the crystal volume, and the specific features of crystallization at the interface of regeneration type. The results presented in this paper may be useful in improving technologies for the production of large BBO single crystals by correcting growth conditions, and optimizing the schemes of cutting them to produce high-quality nonlinear optical (NLO) elements. (c) 2006 Elsevier B.V. All rights reserved.