A report is given of structural investigations on high molecular weight, highly linear polyethylene crosslinked by irradiation with fast electrons in both the molten and the solid state. For the melt-irradiated samples it could be concluded from X-ray measurements that insertion of lattice distortions of the first kind occurs on crystallization.The density of these distortions shows a distinct maximum for an irradiation dose of 25 Mrad. It is assumed, that for lower doses the material crystallizes according to a folding procedure, for higher doses according to a micellar one. For solid state irradiated samples crystalline structure and morphology are not influenced measurably by the crosslinking. The recrystallization behaviour is independent on the dose for the resulting inhomogeneous network.