Several types of deformation bands form during uniaxial extension of Al single crystals for which the tensile axis is initially parallel to . The objectives of the present work are to analyse crystal orientation evolution in the deformation bands and adjoining regions, and to integrate the experimental observations with a crystal mechanics model. The most prominent deformation bands contain secondary slip traces and exhibit crystal rotations consistent with unpredicted slip on a secondary slip system. These special bands of secondary slip (SBSS) become more closely aligned with the tensile axis as extension increases. The evolution of SBSS inclination with extension indicates that SBSS form initially as kink bands and that SBSS boundaries are immobile. SBSS grow during straining by expansion of the volume of material in which secondary slip operates. Deformed matrix (DM) bands are zones between SBSS; primary slip predominates in DM bands. Small intra-DM bands result from spatial variation of the shear amplitudes for the two primary slip systems. The evolution of intra-DM band inclination with extension indicates that intra-DM bands form initially as kink bands and that the band boundaries are mobile, at least to some extent.