Cost and schedule deviation from the estimated baseline are common in construction projects and have a negative effect on construction activity, which is a substantial portion of the GDP in most countries. Previous research studies examined the causes of deviation in several countries including some Gulf Council Countries (GCC) like Kuwait and the UAE, but none were done on the considerable Qatari market, that is set to boom further with the upcoming preparations for hosting Qatar FIFA 2020 World Cup. Therefore, this study identified and ranked, using the relative importance index (RII) method, the significant factors influencing cost and schedule deviation in Qatari residential compound projects. A detailed questionnaire was developed on a Likert scale addressing these factors and was used to solicit the viewpoints of Grade A contractors. The collected project sample had a total capital investment of approximately $1.25 billion and the projects were executed within a five year period (2000–2005). The study indicated that over 85% of the projects experienced cost and/or schedule deviation. Most importantly, the study revealed that most contractors viewed material delays as the most prominent issue influencing construction projects predictability in Qatar. Other top ten factors included design changes, labour shortages, deficient estimates and cash flow planning.