A multilevel assembly system with one type of finished product and several types of components is considered in this paper. The lead times at each level are random discrete variables, and the finished product demand is fixed. The objective is to minimize the holding cost for components and backlogging cost for the finished product. We propose a novel mathematical model which gives the optimal release dates for the components. For a case of a linear supply chain (one type of component at each level) we show that this formulation is equivalent to the discrete Newsboy model. Numerical examples are reported.