The applicability and effectiveness of case-based reasoning (CBR) have been demonstrated in various construction management areas, including bidding, international market selection, safety hazard identification, construction litigation, and preliminary cost estimation. Despite its strong potential as a decision-supporting tool in construction, only a few studies have applied CBR for estimating the preliminary duration that is necessary for the overall success of a construction project. Based on this recognition, this paper develops a CBR model capable of accurately estimating the construction duration in the preliminary stage. The applicability and effectiveness of the developed model are tested through application to 83 multihousing projects. The test results confirm the strong potential of CBR to provide an accurate estimate of construction duration with limited information available in the preliminary stage. This paper is significant in that it provides practitioners with a reliable decision-supporting tool for accurately estimating construction duration, and thus, ultimately increases the possibility of successful project execution. (C) 2015 American Society of Civil Engineers.