The boundary structure of {10 (1) over bar1) deformation twins formed in commercially pure titanium during an initial pass of equal channel angular pressing processing has been studied by transmission electron microscopy (TEM) and high-resolution TEM. A new twinning mode with a twinning dislocation of b(3/3) has been identified using a dichromatic diagram method. The new mode of the {10 (1) over bar1} twin has substantially higher interface energy and accommodates more shear strain during deformation than the conventional b(4) twinning mode. The deviation angle between the habit trace of the twin boundary and the theoretical twinning plane, K1, is dependent upon the density of twin dislocations. (C) 2010 Published by Elsevier Ltd. on behalf of Acta Materialia Inc.