In this paper we present a study on reliability based design of a series-parallel system considering burn-in, warranty and maintenance. The system failure rate function incorporates three different phases of a product life cycle, namely, infant mortality period, the useful period and the wear out period. The system life cycle cost includes costs of burn-in, warranty, installation, preventive maintenance and minimal repair. Genetic algorithms are used to obtain optimal values of system design, burn-in period, preventive maintenance intervals and replacement time. Three distinct cases representing different failure characteristics are studied to investigate the changes in system design and burn-in period for different lengths of warranty. © 1998 Elsevier Science Ltd. All rights reserved.