An outbreak of hepatic photosensitization by ingestion of Brachiaria decumbens is reported in Nelore cattle. After a group of animals (n=320) had been transferred to a pasture of Brachiaria decumbens, several animals began to have diarrhea, 15 showed skin lesions with crust formation, skin cracks, wrinkled and withered, and 80 died. Blood samples, urine and feces of some animals were collected and sent to a laboratory. Hematology showed nonspecific changes and urinalysis and coproparasitologic examination were within acceptable parameters for the specie. Necropsy was performed in one animal. Necropsy findings included greenish brown liver with multifocal lymphocytic pericolangitis with diffuse swelling of hepatocytes, and hepatocytes with marked vacuolization, diffuse bile stasis, presence of birefringent crystals and foamy macrophages. In the kidney, through histopathological examination mild to moderate multifocal tubular nephrosis was observed with presence of hyaline droplets in the lumen of tubules and inflammatory cells, specially macrophages. After diminishing the number of animals, transfer to a pasture with less Brachiaria decumbens, more shaded with trees and treatment with hepatoprotector, antibiotics and topical treatment, animals showed improvement and other cases of photosensitization did not occur. The diagnosis of hepatic photosensitization was based on clinical signs, liver and kidney histopathologic lesions and the reporting of transfer to a Brachiaria decumbens pasture. [ABSTRACT FROM AUTHOR]