In a Croatian outdoor pig breeding unit 32 sows (died between days 2 and 14 post partum) were subjected to gross pathological and further laboratory investigations. Necropsy findings revealed tympany and purple discoloration of the skin, the surface of the livers was dark and had honeycomb appearance with gas bubble infiltrations, congested lungs, hemorrhages, serosanguinous exsudates in body cavities and the stomachs were full. Gram-stains of smears revealed large numbers of Gram-positive rods. Anaerobic cultures yielded high numbers of Clostridium (C.) novyi and fluorescent antibody test (FAT) confirmed this diagnosis. Enzyme immunoassay and toxin testing by neutralisation in Chinese hamster ovary cells revealed toxin B. Based upon the clinical symptoms, gross-pathological signs, bacteriological findings and toxin testing we concluded that C. novyi caused sow mortality. Suboptimal outdoor environment and high outdoor infectious pressure might have contributed the C. novyi caused losses in this unit.