Pravene Nath, MD, Assistant Professor, School of Medicine and Senior Director, Information Technology. NYU Medical Center, a leader in early adoption of CPOE, successfully converted its 25 year-old legacy hospital information system to a modern order entry and documentation suite. Three hospitals, 5000 users, and 700 patients were migrated over 24 hours during one of the largest system conversions undertaken in the US. This presentation addresses the rationale of the big-bang approach, and describes strategies for system design, testing, governance, staffing, communication, marketing, training, activation support, issue management, and post-activation support.