Recent floristic efforts in the Pacific Northwest (PNW) have made it possible to characterize the broad-scale patterns of fern and lycophyte diversity across this geologically-complex region of western North America. The physiography of the PNW has been developing for over 200 million years, but Pleistocene glaciation-induced migrations and recolonizations have strongly influenced the assembly of the flora. With the high dispersal potential of spores, distribution patterns of pteridophytes may represent habitat suitability more than dispersal constraints. Our objective was to describe the biodiversity of pteridophytes in the PNW, determine the spatial distribution of that biodiversity in terms of phylogenetic diversity, identify centers of regional endemism, explore correlations between biodiversity and environmental variables, and infer influences of past glaciation on the pteridophyte flora. We obtained distribution data, constructed a phylogenetic tree using chloroplast data, and used the Biodiverse software package to estimate and map phylogenetic diversity and phylogenetic endemism across the PNW, identifying regions where diversity was higher or lower than expected in comparison to randomization models. Environmental correlates of diversity were identified using principal components analysis with bioclimatic data from WorldClim.org, and we used Maxent to predict habitat suitability for species under past and future climate conditions. We found evidence for the influence of glacial refugia on patterns of pteridophyte diversity, that moisture availability and cold temperatures are strongly correlated with patterns of richness, phylogenetic diversity, and phylogenetic endemism, and infer that topographic complexity may be driving the assembly of the pteridophyte flora indirectly by influencing climate and precipitation patterns.