The effect of surface roughness on a quartz crystal microbalance (QCM) response in contact with a fluid has been investigated. We have combined a perturbation theory approach to the description of the effect of slowly varying interfacial profiles with the scaling analysis for the interfaces including inhomogeneities of a small radius of curvature (bumps and cavities). A relation between the shift of the resonance frequency and the interface geometry has been found. We have discussed the dependencies of the QCM response on the fluid viscosity and on the frequency of the free quartz oscillator. The effect of roughness on the results of adsorption measurements in the QCM experiments has also been studied. It has been demonstrated that the results of QCM measurements can provide valuable information about the interface morphology.