Objective: Our purpose was to determine the clinical effectiveness and cost-effectiveness of three antibiotic regimens for the treatment of pelvic inflammatory disease and tuboovarian abscess. Study Design: A review of all patients' hospitalized at Hutzel Hospital, Detroit, Michigan, for treatment of pelvic inflammatory disease and tuboovarian abscess between Jan. 1, 1993, and April 30, 1997, was performed. Demographic data, antibiotic choices, changes in therapy, operative interventions, and cost of therapy were assessed. Results: Two hundred three patients were admitted for treatment of pelvic inflammatory disease during the study period. We were able to evaluate the clinical efficacy of antibiotic treatment in 179 patients, including 105 patients with pelvic inflammatory disease alone (uncomplicated pelvic inflammatory disease) and 74 women whose infection was complicated by tuboovarian abscess. The three antibiotic regimens evaluated were cefotetan plus doxycycline, clindamycin plus gentamicin, and ampicillin plus clindamycin plus gentamicin. All regimens demonstrated comparable efficacy in treating uncomplicated genital tract infections. Ampicillin plus clindamycin plus gentamicin was significantly better than clindamycin plus gentamicin and cefotetan plus doxycycline in treatment of tuboovarian abscess (p = 0.001). Fifteen women with tuboovarian abscess responded to a change to ampicillin plus gentamicin plus clindamycin antibiotic therapy alone. The hospital stay was prolonged by approximately 3 days in women failing to respond to initial antibiotic therapy, and operative interventions were common in this group of patients. Conclusions: Cefotetan plus oral doxycycline is the most cost-effective regimen for treating uncomplicated pelvic inflammatory disease, whereas triple-antibiotic therapy is the treatment of choice in women with tuboovarian abscess. (Am J Obstet Gynecol 1998;178:1272-8.)