The cold drawing behaviour of a range of polyethylene copolymers was investigated using the technique of simultaneous small-and wide-angle X-ray scattering (SAXS and WAXS, respectively) during deformation. The influence of branch amount, branch length and lamellar population were studied. Branch length was found to be unimportant. Increasing branch content lowered the percentage crystallinity which resulted in an increase in the importance of interlamellar deformation mechanisms. Double yield points were observed in some samples. Molecular and lamellar deformation was totally reversible up to the first yield point, and was apportioned to the activation of fine chain slip. After the second yield point, for which coarse chain slip leading to lamellar fragmentation was held responsible, deformation was irreversible.