Epidemiological, clinical, necropsy and histopathological data were accumulated during the study of 15 outbreaks of Senecio spp poisoning in cattle occurring during the last 3 y in the State of Rio Grande do Sul, Brazil. Morbidity averaged 17% and mortality was virtually 100%. The peak mortality occurred during spring and early summer. The most constant clinical signs included anorexia, depression, tenesmus often followed by rectal prolapse, and rough hair coat. Affected animals remained apart from the rest of the herd, lost weight, presented ascites, and had signs of digestive and neurological disturbances. Icterus, photodermatitis, polydipsia, and dependent subcutaneous edema were occasionally noticed. Two main clinical courses could be distinguished. In the protracted form, progressive weight loss terminated with death within many weeks or months. Alternatively, an acute or subacute course led to death in a few days. In both forms, necropsy and histopathological findings included diffuse fibrosis of the liver, hepatomegalocytosis, and biliary hyperplasia. Extrahepatic lesions included gastrointestinal and mesenteric edema, distension, edema and adenomatoid hyperplasia of the gallbladder, and spongy degeneration of the cerebral white matter. S brasiliensis and S oxyphyllus were the species involved in the field outbreaks.