Prevotella oralis, an obligate Gram-negative anaerobe, was detected as the cause of acute meningitis in a four-year-old cocker spaniel. Clinical signs included acute onset collapse and severe depression. Despite treatment, the animal died. A post-mortem examination was performed which revealed a fibrinosuppurative meningitis with no significant inflammation of the brain or spinal parenchyma. The aetiological diagnosis was confirmed by anaerobic bacterial culture. This report discusses the nature and extent of the lesions and possible routes of infection of the causative organism.