Shear band formation has been observed in (211) left bracket 1 OVER BAR 11 right bracket single crystals of high purity aluminum rolled at 77K. Lamellae of dislocation walls (or microbands) occurred in crystals nearly parallel to one of the active slip planes prior to shear banding. Such microstructures were not observed after rolling at room temperature. The development of microbands is correlated with reduction in dynamic recovery during deformation.