Construction projects, both in developed and developing countries, are widely affected by cost deviations that arise at the completion of the construction process; these deviations manifest themselves as a difference between the executed cost and the planned cost. To mitigate cost deviation, the first step is to identify the causes that originate the phenomenon. Therefore, several studies have been focused on the identification and characterization of the causes that originate the deviations in various countries. However, there is a lack of studies focused on the frequency and severity analysis of the cost deviation causes in the Colombian construction projects. Considering the knowledge gap, this paper presents a frequency and severity analysis of the cost deviation causes in Colombian construction projects by consulting a group of professionals. The research method has four main stages: 1) cost deviation causes identification; 2) questionnaire design, validation, and calibration; 3) questionnaire survey; and 4) frequency and severity analysis. Thirty-eight cost deviation causes were identified, and forty-six professionals from the Colombian construction industry were consulted. The findings show that the three most common causes of cost deviation are: 1) delays of activities, 2) slow permits by local authorities, and 3) unrealistic contract duration. The three most severe cost deviation causes are: 1) slow permits by local authorities, 2) delays of activities, and 3) financial difficulties of the owner.