In large networks, maintaining precise global network state information is almost impossible. Many factors, such as non-negligible propagation delay, infrequent state updates due to overhead concerns, and hierarchical topology aggregation, can affect the precision of the global network state information. In this paper, we investigate the impact of imprecise state information on the performance of dynamic routing and wavelength assignment (RWA) algorithms. We consider single fiber and multi-fiber systems and study dynamic routing with three wavelength selection schemes, namely ˇrst-ˇt, random-ˇt, and most-used. The results show that the precision of global network state information greatly affects the performance of the dynamic RWA schemes. In particular, some RWA algorithms that are traditionally considered as effective algorithms perform poorly in the presence of imprecise global network state information. This indicates that more practical RWA algorithms that can tolerate imprecise state information may need to be developed for large scale optical networks. The results also show that networks with wavelength conversion capability and multi-fiber systems are less sensitive to the imprecise state information.