The large scale structure of poly(methyl methacrylate)-based gels and gel electrolytes has been investigated using small angle neutron scattering. The data reveal two different structural length scales: the shorter being typically 4–25 Å, while the larger is 200–300 Å. Comparison between the gel electrolytes, obtained by doping the gels with lithium salt, and the corresponding salt-free systems shows that the determined length scales are very similar. Thus the dissolved salt has only minor influence on the structure of the polymer network. We also discuss the important relations between structure, dynamics and the performance of the gel electrolytes.