Polyethylene structure has been investigated by energy dispersive X-ray diffraction (EDXD) as a function of temperature below the melting point, via Rietveld refinement. The behavior was studied at four temperatures, namely 25, 40, 70, and 88 degrees C. In this range the structure undergoes a regular volume expansion that may be expressed in terms of specific volume ratio as V-E/V-25 degrees C = 0.991(2) + 4.0(5) x 10(-4) x T(degrees C). The variation is almost completely taken up by the a cell parameter and results, apart for minor intrachain arrangements, in an increased distance between polymer chains.