The mechanism of seeded dispersion polymerization of methyl methacrylate (MMA) was investigated by employing submicron fluorescent polymer particles as seed. These poly(methyl methacrylate) latex particles, containing fluorescent material, were synthesized by a two-step miniemulsion polymerization process and then applied in the seeded dispersion polymerization of MMA. The seed particles were located by tracking the fluorescent signal in the micron-size final particles. The analysis of the final particles showed that most of them contained more than two seed particles. On average, there were 3.7 seed particles in each final particle as obtained under the given conditions of the seeded dispersion polymerization. The location of the seed within the particles being well-separated from each other was considered to indicate that the aggregation of the particles did not occur immediately, but took place after some particle growth had first taken place. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 127: 2635-2640, 2013