During the January 2008, an outbreak occurred in 15 sea bream farms located in Gulluk gulf of Bodrum, Turkey and approximately two million sea breams (Sparus aurata) were died in three weeks. When the outbreak was took place, surface temperature and dissolved oxygen of sea water was measured as 10 C and 7.9 mg/l on January 10, 2008. For pathological examinations, a total of 65 fish (8-9-month-old) were collected from 9 of 15 farms. At necropsy, extreme abdominal distention, milk-like discharge around the anus and depigmentation of skin were observed in all fish. The liver was swollen and yellowish-white in color. Microscopically, degeneration, severe fatty changes and multifocal necrotic areas were observed in the liver. The similar necrotic areas were also noted in the kidney and spleen. Severe verminous enteritis due to Myxidium spp. was seen in two fish farms. The gills were generally edematous and hyperemic. According to result of bacteriological examinations, Vibrio spp. (farm no: 1) and Staphylococcus spp. (farms no: 1, 8) were isolated and identified in some farms. In conclusion, it is thought that the outbreak occurred in sea breams might be winter disease associated with sudden decreases in water temperature together with induced fatty liver.