A construction project is commonly acknowledged as a successful project when the aim of the project is achieved in terms of predetermined objectives of completing the project on time, within budget and to the required quality standard. Delay in the completion of a construction project can be a major problem for the stake holders. These delays lead to costly disputes and adverse relationships amongst the project participants. Civil engineering projects can be delayed due to many reasons. The reasons are related to various types of uncertainties associated with the activities during construction process or during planning and design stages. Therefore, a comprehensive survey was carried out to identify the critical factors that cause delays in Sri Lankan construction projects. From in-depth literature studies, there were 58 causes of delay identified and a questionnaire survey was carried out among 107 selected construction projects in Sri Lanka. The findings show that the delay in Sri Lankan construction projects is mostly originated by labour. This study also explores and provides recommendations to reduce the impact of delays on civil engineering projects in Sri Lanka.