Background: Dengue is a mosquito born flavivirus infection which has been endemic in Sri Lanka since late 19th century. Since there is no effective vaccination to prevent this deadly disease, knowledge of early recognition and appropriate management of the disease and practice of effective vector control are mandatory to control the disease. Method: Hospital based descriptive cross-sectional study was conducted on patients attending the outpatient department (OPD) of the Teaching hospital Peradeniya (THP) from 26th to 31st of January 2015. Data were collected using a standard questionnaire and entered in to a password protected excel worksheet. Statistical analysis was done using SPSS 20. Results: Data from 500 participants (146 males, 354 females) was used for primary analysis. Only 46.4% of the sample had above average knowledge on dengue fever and its vector. Knowledge had a significant association with education level (p<0.01). Overall attitude towards dengue and its prevention was at a higher level. Conclusion: Although the attitude towards dengue was good, knowledge was poor. Hence current health educational programs regarding dengue should be reviewed and also better and effective educational programs should be implemented.