Residual stresses in diamond films grown on WC–Co substrates have been investigated by Raman spectroscopy, x-ray diffraction (XRD), and curvature methods. Microcrystalline diamond films were deposited at 650–700 °C in a conventional hydrogen–methane environment by the microwave plasma-enhanced chemical vapor deposition technique. The film thickness, measured from cross-sectional micrographs taken by scanning electron microscopy, changed from 1.5 to 16.5 μm as the growth time increased from 1 to 12 h. The type and the magnitude of the total residual stress obtained from curvature and XRD measurements agreed very well in all of the samples and changed from tensile to compressive as film thickness increased. However, Raman spectroscopy results showed that all films exhibited compressive stress due to the domain size effect. Different methane fractions, varying from 1% to 3%, have been utilized for diamond growth, and the total residual stress increased as more methane was included.