Code duplication, plausibly caused by copying source code and slightly modifying it, is often observed in large systems.Clone detection and documentation have been investigated by several researchers in the past years. Recently, research focus has shifted towards the investigation of software and process restructuring actions based on clone detection.This paper presents an original definition of a clone classification scheme useful to assess and measure different system reengineering opportunities. The proposed classification considers each group of cloned methods in terms of the meaning of the differences existing between them.The algorithm used for automatic classification of clones is presented together with results obtained by classifying cloned methods and measuring reengineering opportunities in six freely available systems whose total size is about 500 KLOC of Java code.