Purpose This paper aims to analyse the factors affecting the performance of large construction projects in Sri Lanka. The causes, impacts and mitigations in association with the critical factors are explored and discussed. Design/methodology/approach The research focuses on the evaluation and perspectives of clients and contractors of large projects in Sri Lanka. Combined quantitative and qualitative methods were applied in this research. Initially, a questionnaire survey was conducted with clients and contractors involved in large projects to evaluate the factors affecting the performance of projects and to identify the ten most critical factors. Interviews with the clients and contractors of three large projects were conducted to examine the causes and impacts of the critical factors and the approaches used to mitigate them. Findings Significant differences in the factors were observed for more than 40 per cent of the total factors under study, the contractors assigning more weight to most of the factors than the clients. The study identified nine internal factors and one external factor as the critical factors. Of these, seven were related to the contractors, which suggested that the contractors have greater roles in defining performance. Lack of management and technical skills of the parties involved, human capacity, lack of understanding and knowledge of the local context, changes in government policies and political interference were identified as significant causes of the critical factors. Originality/value The study analysed the factors affecting the performance of large projects in Sri Lanka, which, at the time of research, had just ended a 26-year-long civil war and was pushing the construction of large projects to be competitive. The challenges faced in this effort were explored as lessons learnt that might improve the efficiency and effectiveness of infrastructure development in Sri Lanka. The combined quantitative and qualitative methods applied in this study are expected to provide new insights in the project performance research, especially the interviews of the critical factors to gain an understanding on how the factors occurred and manifested themselves in real projects. The findings are, however, expected to be applicable to other developing countries that are currently aggressively developing their large infrastructure.