A gastroenteritis outbreak was observed in the town of Xanthi on Jan 28, 2005. A total of 709 patients (350 males and 359 females, mean age 23.8 +/- 19.95 years) visited the local hospital over a period of two weeks with symptoms of fever (22.3%), abdominal pain (78.6%), nausea (85.5%), vomiting (67.1%) and diarrhea (72.5%). PCR for Norovirus in randomly selected stool specimens examined was positive in all cases (8/8). No other pathogen was revealed. As 85.1% of the primary affected individuals had been using water from a single well (supplying approximately 40% of the 34,889 inhabitants), and water specimens from this well were found to carry a high bacterial load, the waterborne transmission of Norovirus was the main suspected cause of the outbreak. People were advised to consume bottled water and to wash their hands carefully especially after toilet use until the remission of the outbreak. Additionally, more chloride was added to the suspected well (10 ppm or 10 mg/l). Fourteen days later, the outbreak waned and all measures were withdrawn.