Octahedral diamond crystals grown by the temperature gradient method at 1550 degrees C using a BARS apparatus have been studied. Dislocations and planar defects in diamond crystals have been found and characterized by selective etching and X-ray diffraction topography. It is found that the diamond crystals contained not more than four bunches of extended defects. Large planar defects and narrow bunches of straight < 1 1 1 > dislocations extend from the seed crystal. < 1 1 1 > dislocations initiate stacking faults and partial dislocations in the < 1 1 2 > direction. These defects also give rise to < 2 2 1 > dislocations. Partial dislocations are dominant. Screw and then edge and mixed dislocations appear as the densities of linear and planar defects increase in the bunch. Combined cathodo- and photoluminescence topographic, X-ray topographic and selective etching studies of {1 1 1} faces showed, that single < 1 1 1 > dislocations are the sources of large low-elevation hillocks, which appeared during crystal growth. It is concluded that diamond crystal growth at the specified average rates of 39-45 mu m/h is a phenomenon involving the simultaneous participation of dislocations and two-dimensional nucleation as sources of growth steps. The studies have shown that dislocation-free regions in the octahedral diamond crystals weighing 3 carats occupy about 58 mm(3), and some crystals have completely dislocation-free {1 1 1} growth sectors. (C) 2011 Elsevier B.V. All rights reserved.