Five adult female Eld's deer died acutely or were euthanatized because of clinical signs including anorexia, signs of depression, and uremia. On necropsy, these deer had large masses of necrotic abdominal fat constricting the ureters, causing hydroureter and hydronephrosis. The herd from which these deer originated was maintained on pastures consisting primarily of tall fescue, samples from which were subsequently confirmed to be infected with an endophytic fungus that is known to cause similar lesions in cattle. A retrospective study of deaths in this herd revealed a sharp increase in incidence of abdominal lipomatosis since 1994. Physical examinations on the herd revealed > 90% of females to be affected. Endophyte-infected tall fescue forage was concluded to be a major factor in the development of lipomatosis in these deer. Other contributing factors were considered. Lesions caused by endophyte-infected fescue can be severe, and this disease can develop in nondomestic species.