This paper describes the PID Evaluation and Clinical Health Study (PEACH), a multicenter, randomized clinical trial designed to compare treatment with outpatient and inpatient antimicrobial regimens among women with pelvic inflammatory disease (PID). PEACH is the first trial to evaluate the effectiveness and cost-effectiveness of currently recommended antibiotic combinations in preventing infertility, ectopic pregnancy, chronic pelvic pain, recurrent PID, and other health outcomes. It is also the largest prospective study of PID ever conducted in North America. We describe the PEACH study's specific aims, study organization, patient selection criteria, conditions for exclusion, data collected upon entry, randomization and treatment, adherence measures, follow-up activities, quality-of-life measures, outcomes, and statistical analyses. In the first 11 months of enrollment (March 1996-January 1997), 312 women were randomized. Of eligible women, 59% consented to enroll. Participating women are primarily black (72%) and young (mean age 24 years). After a median of 5.5 months of follow-up, we were in contact with 95% of study participants. The PEACH study will provide a rationale for selecting between inpatient and outpatient antibiotic treatment, the two most common treatment strategies, for PID.