Comments are valuable especially for program under- standing and maintenance, but do developers comment their code? To which extent do they add comments or adapt them when they evolve the code? We examine the question whether source code and associated comments are really changed together along the evolutionary history of a soft- ware system. In this paper, we describe an approach to map code and comments to observe their co-evolution over mul- tiple versions. We investigated three open source systems (i.e., ArgoUML, Azureus, and JDT Core) and describe how comments and code co-evolved over time. Some of our find- ings show that: 1) newly added code--despite its growth rate--barely gets commented; 2) class and method decla- rations are commented most frequently but far less, for ex- ample, method calls; and 3) that 97% of comment changes are done in the same revision as the associated source code change.