A monthly shorebird census in Mondego estuary, Portugal was made during ten years (1993-2002) and the information adds to the midwinter census carried out at international level. It is shown that higher variability in shorebird community occurred during the breeding and migrating periods, while the winter assemblage was very similar among years. The study provides precise information of the importance of the Mondego estuary, and the trends and phenology of its shorebird community. Six species are responsible for a large proportion of the total abundance throughout the year. Dunlin (Calidris alpina) is the most abundant species, followed by the Avocet (Recurvirostra avosetta). Over the study period, there was a significant increase in the total number of shorebirds that occur in some months. This was mainly due to the increase of the main species, the Dunlin. Only the Avocet showed a significant decrease in abundance. These trends were not explained by changes in overall flyway population or the Portuguese totals. Therefore, local explanations need to be considered (e.g., changes on habitat quality).