Polymicrobial aerobic and anaerobic flora are responsible for pelvic inflammatory disease (PID). The most frequent pathogens appear to be Neisseria gonorrhoea and anaerobic bacteria (most commonly anaerobic cocci and Bacteroides sp.). Recent studies have demonstrated the recovery of Chlamydia trachomatis in up to a third of these infections. Although N. gonorrhoea is frequently recovered from cervical cultures, it is less commonly recovered from intra-abdominal sites. Recent studies have demonstrated the in-vivo synergistic relationship between N. gonorrhoeae and Bacteroides fragilis. The growth of each component of the mixed infection was enhanced when these were present together in an abscess. Furthermore, the emergence of encapsulated strains was enhanced in these infections. This synergy enables the organisms to cause more severe local and systemic damage to the host. Therapeutic intervention should include the use of antimicrobial agents effective against both the aerobic and anaerobic components of the mixed infection. Unless such therapy is given, the infection may persist. It is also recommended to use antimicrobials that possess synergy between them against the bacterial pathogens. Agents effective against the anaerobic pathogens are metronidazole, clindamycin and cefoxitin. Antimicrobials effective against the Gram-positive aerobic pathogens and N. gonorrhoeae are spiramycin and penicillins. Aminoglycosides or third generation cephalosporins are effective against Gram-negative enterics. The combination of metronidazole and spiramycin has shown to be synergistic against mixed infections of Bacteroides sp. and N. gonorrhoeae.