Tyzzer's disease, caused by Bacillus piliformis and characterized by a multifocal, necrotizing hepatitis was diagnosed in a 25 days old, male, German warmblood foal. The animal was submitted to the clinic of horses because of colic symptoms and a severe depression. Upon arrival it was comatose, recumbent and showed opisthotonos. Due to a severe, metabolic acidosis and a rapid progression of the disease, the foal was euthanatized. In immediately formalin-fixed tissue samples Bacillus piliformis was detected in the cytoplasma of hepatocytes by different histological techniques (Giemsa stain, silver impregnation technique by Warthin-Starry, immunohistology). This case is discussed within a literature review.