Plastic deformation of uniaxially oriented polyethylene (PE) fiber has been examined by small and wide angle synchrotron X-ray scattering. Morphology changes of the lamellar stack with deformation beyond yielding have been characterized and quantified. Atomistic simulations of tensile deformation of the lamellar stack in the longitudinal direction compare favorably to the experimentally observed morphological changes in the PE fiber. Experimental deformations at 100 degrees C exhibit responses comparable to those observed by simulation of deformation with constant total volume at 77 degrees C and a strain rate of 5 x 10(6) s(-1). Experimental deformations of the PE fiber at 25 degrees C were found to be comparable to simulated tensile deformation with constant lateral dimensions at 77 degrees C and a strain rate of 5 x 10(7) s(-1). Cavitation in the interlamellar region was found experimentally in the PE fiber deforming at room temperature as predicted by simulation with constant lateral dimensions at the higher strain rate. Melting, recrystallization, and removal of entanglements observed in the PE fiber deformation at 100 degrees C agree with the simulation results of a constant volume deformation at the slower strain rate. The ability to define the deformation behavior of PE at room and at high temperatures through simulation offers unique opportunities to examine how the interlamellar amorphous topology affects PE deformation.