A patient with chronic, unilateral conjunctivitis is presented. The predominant bacterial flora consisted mainly of Prevotella intermedia (formerly Bacteroides intermedius) and Peptostreptococcus micros. Restriction endonuclease fingerprinting of genomic DNA demonstrated that P. intermedia most probably originated from the oral cavity. In the oral cavity this species was recovered from the dorsum of the tongue, the tonsillar area and the periodontal pockets. Topical treatment with various antibiotics had failed to cure the infection in the past. The condition was cured after systemic therapy with metronidazole and amoxicillin.