Background This paper describes and assesses the electronic surveillance of outbreaks based on the early warning for four endemic diseases – typhoid fever, amebic dysentery, viral hepatitis A and brucellosis – in Lebanon, for the first 28 weeks of 2005 and first 26 weeks of 2007. Methods The electronic early warning system is based on the mandatory notification of 37 targeted diseases. The four target diseases assessed in this paper are based on monthly notification. Standards were set for case definitions and forms. Physicians and hospitals report to the Ministry of Public Health (MOPH), where data is checked and transmitted to a central location for entry into the national database, which stores historical and current data, as well as population estimates based on national surveys. The event date was selected for case dating. Indicators triggering abnormalities include number of cases, rates, and relative ratios. Four relative ratios were selected using the period of 1 week, 4 weeks or 52 weeks for the current and previous years. Screening was conducted on a weekly basis in 2005, and on a daily basis in 2007. Abnormal signals were verified, documented and grouped by alert-episodes for each disease, district, and period. MOPH teams verified and investigated case clustering. Results During the first 28 weeks of 2005 and the first 26 weeks of 2007, screening operations were 68% and 89%, respectively, for completeness. Detected abnormal signals were 26 and 166 and identified alert-episodes were 11 and 22, respectively. Verified clusters were 7 and 11; positive predictive value for clusters identification was 64% and 50%, respectively. The time interval between first cases and first abnormal signals was on average 4 weeks and 5 weeks, respectively. Conclusion Timely reporting, transmission, data entry, analysis and communication are the elements of timely outbreak detection. The electronic surveillance of outbreaks for epidemic-prone diseases, which are mandatory notified on a monthly basis using indicator-based thresholds, is capable of detecting spatio-temporal clusters and outbreaks; however, with some delay. The national surveillance system needs to be reviewed in order to provide timely data for early warning surveillance and response.