This paper addresses the design, technical implementation and field experiences of using a Web-based data management system (DMS) for the GirlTalk for Teen Moms Study, being conducted in the NIH-DC Initiative to Reduce Infant Mortality in Minority Populations in Washington, D.C. (NIH-DC Initiative). The primary objective of this multi-site randomized clinical trial is to evaluate the effectiveness of a community-based intervention for minority teen mothers with the primary purpose of reducing subsequent teen pregnancies. The DMS monitors all activities for screening, recruitment, enrolment, in-depth interviews, randomization, interventions, repeated measures, outcomes, adverse events and follow-up activities for each participant over the course of their two-year enrolment in the study. Field staff from multiple sites use the DMS to manage over one hundred possible activities with a complex series of triggers that lead from one activity to the next. The steps taken in designing the DMS, its technical implementation and the lessons learned from experiences in the field are presented. Previous studies in the NIH-DC Initiative utilized a PC-based data management system requiring nightly data transmissions to and from each site to synchronize study data. This Web-based DMS is compared with the earlier PC-based systems, and the efficiencies obtained are described, including real-time data access, simplified software management, data security, and anytime/anywhere access for all users. Cost considerations are outlined for the web-based DMS versus the PC-based system in terms of study size, study duration, number of sites and technical infrastructure. Several features of the DMS are discussed, including the role-based menu, events tracking, appointment scheduling, shared calendars, report generation, access to study documents, and uploading of data files to RTI secured servers. Lessons learned are discussed based on our field experiences and user feedback during the first year of implementation.