The economic impact of the greenhouse thrips, Heliothrips haemorrhoidalis (Bouché) (Thysanoptera: Thripidae), has increased on Chilean avocados as a consequence of the high value of the crop and the increased injury to the fruit surface. The population dynamics, phenology, and patterns of aggregation of H. haemorrhoidalis was determined with the objective of rationalizing the use of pesticides using a therapeutic control approach. The study was conducted in 2 avocado fields during 2005 to 2007 in the Valparaiso Region of Chile. New colonies developed on the leaves and small fruits, reaching greatest numbers at the beginning of the winter months. Immature stages were greater in number than the adults during most of the production season. The spatial distribution was calculated using Taylor's power law, showing an aggregated pattern with indices of 1.46 and 1.53 on leaves and fruits, respectively. Pooled data were used to describe the relationship between population density and the proportion of infested leaves and fruit. In the case of a density of about 2 thrips per leaf or fruit, the proportion of infested samples was 0.8. Sample size curves were generated as a function of mean density of thrips with about 20 presence/absence samples needed to estimate densities of 0.5 thrips or more at a precision level of 25%.