Replication is a key strategy for improving locality, fault tolerance and availability in distributed systems. The paper focuses on distributed file systems and presents a system to transparently manage file replication through a network of workstations sharing the same distributed file system. The system integrates an adaptive file replication policy that is capable of reacting to changes in the patterns of access to the file system by dynamically creating or deleting replicas. The paper evaluates the efficiency of the system in several situations and shows its effectiveness.