Often, the only sources of information about the evolution of software systems are the systems themselves and their histories. Version control repositories contain information on several thousand of files and on millions of changes. We propose an approach based on dynamic time warping to discover change-patterns, which, for example, describe files that change together almost all the time. We define the Synchrony changepattern to answer the question: given a software system and one file under modification, what others files must be changed? We have applied our approach on PADL, a software system developed in Java, and on Mozilla. Interesting results are achieved even when the discovered groups of co-changing files are compared with these provided by experts.