The Girls health Enrichment Multi-site Studies (GEMS) was a multi-center research program created for the purpose of testing interventions designed to prevent excess weight gain by African-American girls, as they enter and proceed through puberty. However, GEMS was not a "multi-center clinical trial" in the usual sense. Although these studies applied similar eligibility criteria, observed a similar follow-up schedule, and followed a similar measurement protocol, important differences existed, as well. Each field center developed its own intervention(s) and corresponding control, and tailored its study to the specific hypothesis being tested. Therefore, the study populations were somewhat different, with recruitment strategies that varied accordingly, and supplemental evaluations appropriate to the specific interventions were conducted on a site-specific basis. The purpose of this paper is to describe the common design elements of the GEMS Phase 1 pilot studies. This report presents the basic study design, a brief overview of the interventions, the measurements taken and their rationale, and procedures both for compiling the collaborative database, and performing site-specific analyses.