We have studied intensity profiles of Kossel's lines from the (111) planes of natural diamond single crystals, synthetic diamond single crystals grown in the Ni-Mn-C and Ni-Mn-C+Boron growth systems as well as from diamond crystals grown by the temperature gradient method. The halfwidth of the lines from the (111) planes of the type Ia natural diamond single crystals is the minimal and for the most perfect crystals is 0.02°. The half-width of the lines from crystals produced in the Ni-Mn-C growth system increases up to 0.05°. An increase in the half-width of the Kossel line characterizes the diffuse scattering of X-radiation and can be used to define diamond structural characteristics.