We present an algorithm that computes the edit distance of two RNA structures with arbitrary kinds of pseudoknots. A main benefit of the algorithm is that, despite the problem is NP-hard, the algorithmic complexity adapts to the complexity of the RNA structures. Due to fixed parameter tractability, we can guarantee polynomial run-time for a parameter which is small in practice. Our algorithm can be considered as a generalization of the algorithm of Jiang \etal~\citeJiang2002 to arbitrary pseudoknots. In their absence, it gracefully degrades to the same polynomial algorithm. A prototypical implementation demonstrates the applicability of the method.