The objective of this study was to use successful quality improvement initiatives in large multispecialty medical groups to identify the organizational factors that were the most important to improvement. The study analyzed the most successful quality improvement initiatives from those submitted by the 24 members of the Council of Accountable Physician Practices. Twelve initiatives from 8 groups were selected that met the study criteria for large improvement for large numbers of patients. An independent group used these initiatives to identify potentially important factors and then asked key local leaders to rate the importance of these factors on a scale of 1 to 4, importance rating (1-4 scale) for each of 18 identified factors. Eighteen factors were identified and 5 stood out as ranked a 4 (Very Important) for at least 80% of the initiatives: Communication, Use of Evidence-Based Medicine, Leadership, Measurement, and Reporting. Another 7 of the 18 factors were ranked a 4 for more than 50% of the initiatives. All the factors are related to the 6 challenges in the Institute of Medicine report. It was concluded that any organization striving to greatly improve the quality of its healthcare delivery should consider these factors when planning improvement initiatives.