Project delays and cost overruns are both a global phenomenon and a common problem in construction projects. Private developers and local authorities are facing increasing costs and delays to their projects. This means that budgets and schedules are exceeded. The fact that the same issue affects all parties involved in the construction industry, whether private or public, shows how big this problem is. Based on a survey of 309 experts from the DACH region, this study identifies the most relevant causes of project delays and cost overruns. The results of the study indicate that, despite some similarities, different expert groups, such as planning offices and construction companies, view different factors as having the greatest impact on project delays or cost overruns. Project managers, contractors and clients involved in planning and construction can use the results of this study to supplement their project risk analysis. This could help identify potential risks in the various project phases and therefore minimize their impact if they occur.