The gelation of a polymerizing microemulsion system has been studied using Brillouin light scattering. The time dependences of the Brillouin shift and width suggest that the polymerization process occurs in two stages, with the second stage starting at the onset of gelation. The behaviours of the Brillouin shift and width during the second stage are explained in terms of a relaxation-time model. A scanning electron micrograph of the completely polymerized microemulsion sample reveals the existence of microporous structures.