The reliability of a computer-based system may be as important as its performance and its correctness of computation. It is worthwhile to estimate system reliability at the conceptual design stage, since reliability can influence the subsequent design decisions and may often be pivotal for making trade-offs or in establishing system cost. In this paper we describe a framework for modeling computer-based systems, based on the Unified Modeling Language (UML), that facilitates automated dependability analysis during design. An algorithm to automatically synthesize dynamic fault trees (DFTs) from the UML system model is developed. We succeed both in embedding information needed for reliability analysis within the system model and in generating the DFT. Thereafter, we evaluate our approach using examples of real systems. We analytically compute system unreliability from the algorithmically developed DFT and we compare our results with the analytical solution of manually developed DFTs. Our solutions produce the same results as manually generated DFTs. Keywords: Dynamic fault trees, Fault tree synthesis, Reliability analysis, UML