PurposeCost overruns have been identified as the most significant challenge for construction sector stakeholders. Like many developing countries, the Iranian construction industry suffers from poor cost performance. So, the current research aims to investigate the causes of cost overrun in Iranian construction projects. This paper also reviews the findings of similar studies conducted in several Asian countries.Design/methodology/approachThis paper includes a literature review and a quantitative method with a questionnaire survey. The review is limited to the studies investigating the causes of cost overrun in an Asian country in the last decade. Moreover, the current research was conducted through a questionnaire prepared based on 43 common factors identified through the literature review. The required data were gathered from the representatives involved in handling construction activities in Iran. The collected data were analyzed based on relative importance index (RII), using the SPSS software package.FindingsThe results showed that poor site management, improper planning, fluctuation of prices of materials, lack of experience, and poor economic condition are the critical reasons for cost overrun in Iranian construction projects. The findings also indicated that among the studies conducted in Asian countries, the first three factors have the highest frequency.Originality/valueThis paper highlighted most studies concerning the cost overrun factors in construction projects in different Asian countries in recent years. Up-to-date knowledge helps to understand the complexity of this field in various periods and therefore minimizes the risk of cost overrun. This research can also be used as a benchmark for further studies to clarify similar issues in other developing countries.