Geotechnical risks are ubiquitous and of paramount significance, as they can result in cost and time overruns in infrastructure projects. The purpose of this study is to assess the importance of geotechnical risks in terms of their cost and schedule impacts. To achieve this purpose, cost impact index (CII), schedule impact index (SII), and frequency index (FI) of geotechnical risks, which were determined through a literature review, were used to specify the importance level of each risk. A survey was conducted with the participation of 47 professionals from the heavy civil construction sector in Turkey. Importance index theory was adopted to estimate the importance of each risk in terms of cost and schedule. The differences in perceptions of respondents, in the context of cost and schedule, were assessed using correlation analysis. The findings indicate that there were no significant differences in the perceptions of respondents about the impacts of geotechnical risks on cost and schedule, and “soft clays, organic silts, or peat” was found to be the most significant risk factor when both impact and frequency are considered concurrently. The findings of this study can be used by industry professionals or governmental agencies dealing with infrastructure projects to identify the reasons for time and cost overruns with respect to the geotechnical conditions.