Occurrence of variation orders (VOs) is a common phenomenon in building projects and a challenging feature. Opinions and feedback of the stakeholders of building projects at Khartoum State – Sudan were investigated to identify and rank the key factors that cause VOs and evaluate their consequent impact on projects’ performance. 10 projects were thoroughly analyzed to determine how their performance was affected by the occurrence of VOs and in conjunction with this an industry wide survey that was conducted to determine the frequency of occurrence of a previously compiled list of factors. 130 respondents -contractors, consultants, projects’ owners and project managers-took part in the survey. Considering the frequency of occurrence and the strength of their impact, the relative importance index from the participants’ feedback was calculated allowing the ranking of the factors causing VOs. It was found that the main causes for VOs emerged from the owners’ side and are mainly attributed to changing his needs or scope of work. It was also confirmed that there is a significant relationship between the occurrence of VOs and projects’ time extension (by 22-200%) and cost overrun (by 2.67-42.86).