Abstract. Construction activity requires major investment outlays in most developing countries;
moreover, most construction projects in these countries are characterised by overruns in cost. In an
attempt to identify the factors for such overruns, a descriptive survey was carried out in a typical
developing country, Turkey. Relative Importance Index method was used to analyse the quantitative
data. The analysis of 40 sub-factors considered in a survey indicates that the main factors affecting
cost overruns in the construction of residential projects of Turkey are, improper planning, inaccurate
project cost estimation, high cost of needed resources (money, men, materials and machinery), lack of
skilled workforce, price of construction materials and high land prices. The relative levels of impact of
the identified are expected to guide the project team and owners / clients in addressing the factors in a
cost-effective manner