The diffusion of acetophenone in peroxide cross-linked low-density polyethylene (LDPE) medium-voltage cable was investigated with Fourier transform infrared (FTIR) microscopy. The influence of storage under normal climate and for up to 2 years on the acetophenone profile are discussed. The diffusion rate and the coefficient of diffusion of acetophenone in cross-linked LDPE were determined. It could be shown that the coefficient of diffusion is independent of the morphology of the medium-voltage cables investigated.