Kinetics of controlled radical polymerization (CRP) is examined in a dispersed medium, when the persistent radical effect operates. For that purpose, nitroxide-mediated CRP is considered in a miniemulsion system with oil-soluble alkoxyamine unimolecular initiator and in the absence of thermal self-initiation. An analytical expression of the rate of irreversible termination is proposed as a function of particle size, and it is compared with the rate of termination in bulk. From these expressions, the evolution with monomer conversion of the concentration of released nitroxide is calculated. For large particles, the polymerization kinetics was found to be similar in bulk and in the miniemulsion. In contrast for small particles, owing to slower terminations, the concentration of released nitroxide was shown to be smaller in the miniemulsion than in bulk, leading thus to a lower proportion of dead chains, a faster polymerization, and a broader molar mass distribution.