Investigation into the causes for low IT project success rates has dominated both the IT project management literature and the focus of IT project management professionals for decades. Many factors, including a variety of hard skills and soft skills, have been proposed to have an effect on IT project success. This study presented 142 such factors, collected from the IT project management literature over the past 25 years, to members of the Project Management Institute in an effort to ascertain which of these factors had the most impact on IT project success in their respective organizations. Factors were classified into 5 groups: Communication Group, Project Manager/Team Group, Project Group, Organization Group and User Group. Results indicated that 71.8% of respondents agreed that Ability to Communicate at Multiple Levels from the Project Manager/Team Group was the most important factor critical to IT project success of the 142 factors under consideration.