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Two-dimensional dislocation dynamics (2D-DD) simulations under fully periodic boundary conditions are employed to study the relation between microstructure and strength of a material. The material is modeled as an elastic continuum that contains a defect microstructure consisting of a preexisting dislocation population, dislocation sources, and grain boundaries. The mechanical response of such a material is tested by uniaxially loading it up to a certain stress and allowing it to relax until the strain rate falls below a threshold. The total plastic strain obtained for a certain stress level yields the quasi-static stress–strain curve of the material. Besides assuming Frank–Read-like dislocation sources, we also investigate the influence of a pre-existing dislocation density on the flow stress of the model material. Our results show that – despite its inherent simplifications – the 2D-DD model yields material behavior that is consistent with the classical theories of Taylor and Hall–Petch. Consequently, if set up in a proper way, these models are suited to study plastic deformation of polycrystalline materials.