We investigated diving beetle (Dytiscidae) assemblages in twelve wetlands in an agricultural landscape in southeastern Sweden. Beetles were trapped in wetlands that varied in permanence (temporary or permanent), area (25 to 4,800 m²), age (11 to >50 yr), and shading (open to wooded surroundings). Our objective was to determine if those environmental factors are important in structuring the local assemblages of diving beetles and how the combination of different types of wetlands influence the diversity of diving beetles in a landscape. Generally, species-area relationships were weak, and shaded wetlands, both permanent and temporary, of intermediate size (240–1,100 m²) had the highest richness after a rarefaction analysis. It was not possible to discern a certain type of wetland where diversity was highest (measured by index α and Shannon-Wiener's index), although, again, intermediate sized wetlands did tend to be more diverse than others. Similarities in species compositions were highest among environmentally similar wetlands, and assemblage structure differed substantially between different types of wetlands. Results of ordination (CCA) and variance partitioning revealed that permanence and degree of shading were the most important factors in structuring assemblages. Our findings imply that high diversity of the diving beetles depends on the number of wetland types represented in a landscape. It is possible to achieve high diversity in a small area by combining permanent and temporary wetlands, as well as many age and successional stages, located in wooded and open environments.