Dengue virus (DENV) infection has been endemic to Sri Lanka and reliable estimates of burden of disease are limited. Such information is crucial for prevention and control of the disease and for vaccine introduction. We are conducting a community based enhanced passive surveillance study to estimate burden of DENV infection and disease. The study is based on a one year follow-up cohort of 800 randomly-selected children aged <12 years in a municipality ward of Colombo, Sri Lanka. The baseline blood samples tested by IgG capture ELISA indicate that the flavivirus seroprevalence in the cohort is 52% (ranges from 14% below 1 year to 72% at 12 years). These results suggest endemic transmission of DENV among children in Colombo.