A total of 116 freshwater diatom taxa, belonging to 22 genera were observed in five aquatic and nine relatively dry moss samples from Hopen Island (Svalbard). The genera Navicula, Pinnularia and Eunotia had the highest diversity of taxa. A hierarchic-agglomerative cluster analysis revealed the occurrence of three major diatom assemblages. The Tabellaria flocculosa - Navicula brekkaensis var. brekkaensoides assemblage was found in all shallow pools of the area. The Hannaea arcus assemblage was typically associated with running water as it was observed in a small brooklet and on mosses that were drying after having been flooded. The Eunotia praerupta - Pinnularia intermedia assemblage occurred in mosses. Differences are described between the diatom composition of the aquatic and the moss samples.