The paper presents a method to compute performance metrics (response time, sojourn time, throughput) on Unified Modeling Language design. The method starts with UML design annotated according to the UML Profile for Schedulability, Performance and Time. The UML design is transformed into a performance model where to compute the referred metrics. Being the performance model a Stochastic Well-formed Net, the method is enabled to analyze systems where the object identities are relevant as well as those where they are not. A complete case study reveals how to apply the method and its usefulness. Ó 2007 Elsevier Inc. All rights reserved.