In this paper we investigate to what extent the occurrence of foliar diseases is affected by plant relative abundance in the understory community of the Los Tuxtlas tropical rain forest, how this changes with season of the year, and how plant species with different life histories present at the understory are affected by disease. To provide a context to these analyses we also include a general description of the floristic composition of the understory community. Using the eight most common species, we found that their relative abundance in each sampling location significantly explained the proportion of diseased plants. Accordingly, using the relative abundance of all plant species, we found that the probability of a host plant species being free of infection showed a significant decrement with abundance. At the plant level, we found that relative abundance had the greatest effect on the variation in leaf area/plant affected by pathogens, although the proportion of explained deviance was only 12%. Seasonality did not affect disease incidence and disease levels per plant. Throughout the year, plant relative abundance was very much lower in lianas, tree seedlings, and palms than in perennial herbs and ferns, and disease incidence was very much higher in the latter two, the most abundant life forms. These results collectively suggest that both intraspecific and interspecific variation in plant relative abundance explain variation in leaf damage by pathogenic fungi in tropical forest understories.