The main aim of this paper is to identify the main causes for the delays in the Portuguese construction industry and its impact, with the purpose of increasing knowledge on the causes and impacts of delays in construction projects. The Relative Importance Index was adopted to classify the importance of the 47 causes and six impacts identified causes of delays. Results show the main causes of delay are slow decision-making, changes to orders, unrealistic timescales and poor contract specifications, financial constraints on the contractor and the type of bidding and contract award process. The main impacts are time and cost overruns and disputes. Factor analysis revealed eight high-level causes that result in 26 of the original causes. Finally, Pearson correlation coefficients were calculated to find the relationship between the extracted factors (latent causes) and impacts, revealing that lack of commitment and substandard contracts are positively correlated with all impacts, and poor consultant performance is negatively correlated with time overrun. These findings are expected to improve the scientific community's knowledge of construction management.