Cytophaga psychrophilia, the causative agent of cold-water disease, is an important pathogen of cultured salmonid fishes. Most often, the bacteria infects the external surfaces, causing ulceration of the dermis and necrosis of the underlying muscle. We will present an unusual manifestation of this disease observed in fingerling rainbow trout reared at a state hatchery in Pennsylvania. Mortalities began at around 50 fish per day in affected raceways and the only external lesions were pale gills, occasional bilateral exophthalmia and abnormal (misshapen) snouts. Internal organs were also pale. Within 4 days, mortalities reached 200 per day and some fish were observed swimming in circles. Histologically, chronic periostitis, osteitis, meningitis and ganglioneuritis were observed. Although the reaction was primarily present in the cranial area, pockets of inflammation and cartilage necrosis were found along the vertebral column. The deformed snouts were a manifestation of cartilage necrosis and a massive inflammatory reaction. Long, thin, gram - bacteria were observed within this inflammatory response. None of these fish ever showed the typical external ulcerations usually associated with cold-water disease.