<p>This paper aims to optimize the frequency of maintenance related to tree trimming in distribution networks, while simultaneously minimizing maintenance costs and penalties associated with violations of reliability targets. The reliability-centered maintenance model used in this paper is based on a chronological predictive reliability analysis that estimates the penalties through a combination of the following approaches: non-sequential Monte Carlo simulation, time domain solution, and state aggregation techniques for Markov chains. Multi-objective particle swarm optimization was used to solve the multi-criteria optimization model associated with tree trimming scheduling. The main contributions of this paper to the literature are the modeling of the temporal evolution of reliability indices, based on time domain simulation, and the expansion of conventional predictive reliability assessment programs to incorporate degradation process through state aggregation techniques. Tests results demonstrated that the proposed reliability-centered maintenance approach reduces penalties by half with a high cost/benefit ratio.</p>