Strain and misfit dislocation density in small-area Si1-xGex films grown by selective low-pressure chemical vapour deposition on Si(100) have been investigated as a function of lateral size by Rutherford backscattering spectrometry, ion channeling, photoluminescence spectroscopy and transmission electron microscopy. The results show that a large-area Si0.84Ge0.16 film with a thickness of 430 nm has relieved more than 60% of the pseudomorphic strain by formation of misfit dislocations while 100 x 100 mu m(2) square-shaped structures exhibit full pseudomorphic strain. In comparison to large-area growth, a significant decrease of the dislocation density was already observed in structures as large as 5000 x 300 mu m(2). The experimental results are in good agreement with theoretical estimations assuming a fixed density of nucleation sources. Selective growth and size-dependent reduction of the dislocation density may be important regarding future device applications and low dimensional semiconductor heterostructures as quantum wires and quantum dots based on the Si/Si1-xGex materials system.