Abstract: Software designs decay as systems, uses, and operational environments evolve.  As software ages the original realizations of design patterns may remain in place, while participants in design pattern realizations accumulate grime – non-pattern-related code.  In this talk I discuss the extent to which software designs actually decay, rot and accumulate grime by presenting research about the aging of design patterns in successful object oriented systems.  By focusing on design patterns we can identify code constructs that conflict with well formed pattern structures.  Design pattern rot is the deterioration of the structural integrity of a design pattern realization.  Grime buildup in design patterns is a form of decay that does not break the structural integrity of a pattern but can reduce system testability and adaptability.