Clindamycin has been extensively used in the therapy of obstetric and gynecologic infections for over 20 years. This antibiotic is well known for it activity against anaerobic bacteria, particularly beta-lactamase-producing strains of the Bacteroides species. Clinicians should also recognize its very good activity against aerobic gram-positive cocci, such as the group B streptococci, but be aware of its absence of activity against aerobic gram-negative rods, such as E. coli. In combination with an aminoglycoside, clindamycin has become the standard by which other antimicrobials have been judged in the treatment of pelvic infections. A dose of 900 mg administered intravenously every 8 hours is recommended when treating the serious infections discussed. Although concern about the potential side effect of pseudomembranous colitis is valid, in practice, this is an uncommon problem that responds well to the discontinuation of clindamycin and to the treatment of the C. difficile-induced condition with vancomycin or metronidazole.