An important difficulty in the field of maritime engineering is the probabilistic nature of wave drivers. To quantify the magnitude of forces that a structure will be exposed to in its lifetime, a maritime engineer needs to have a good understanding of the extreme climate of the region. By conducting extreme wave analyses on previously gathered wave data one can estimate design values, but there will always be uncertainty present. The objective of this paper is evaluating that uncertainty. More specifically, we will formulate conclusions about the uncertainty that lies in the model as well as the method that is used to conduct the analyses. But the latter is also influenced by regional particularities. In order to have a better view on those regional particularities, we conducted our investigation with data from two distinct maritime environments: the NW Mediterranean and the Southern North Sea. A last point of interest is the effect of the amount of the recorded data on the uncertainty within extreme wave analyses. We will do this by conducting extreme wave analyses on well-chosen datasets: developed with different selection methods, representing different time periods, having different sizes. It will therefore be necessary to establish storm databases for both regions and with different methods. Besides conducting non-directional and directional wave analyses, we also look into other storm characteristics. The results presented in this paper do not only give additional insights in the way to conduct extreme wave analyses, but will also provide more insight in the storm behaviour of both regions, the evolution of storm characteristics in the past two decades and its implications on the uncertainty in extreme wave analyses.