A cross-linking polymerization of hydrophobic monomers within the surfactant bilayer of vesicles leads to the formation of a quasi-two-dimensional polymer network. Depending on the dimensions of the templating vesicles, polymer hollow spheres can be produced with diameters ranging from several tens of nanometers up to hundreds of micrometers. The hollow sphere morphology of the polymer particles is proved by confocal laser scanning microscopy, scanning electron microscopy, and static and dynamic light scattering. After extraction of the surfactant matrix, the polymer particles contract considerably without loss of their spherical shape. The extend of the contraction depends sensitively on the crosslinking density of the polymer network and shows a similar scaling behavior as branched polymers.