This article addresses the research question: How is uncertainty affecting project portfolios managed in dynamic environments? The management of four portfolios was studied in two large multidivisional corporations. The portfolios were characterized by a high degree of uncertainty and many interdependencies between the projects. The results of this research indicate that the sources of change go beyond the two groups identified in The PMI Standard for Portfolio Management (Project Management Institute, 2006), that is, (a) Portfolio Performance and (b) Business Strategy Changes. The sensing mechanisms put in place by both companies primarily addressed uncertainty related to project scope.