A simple optical method to estimate the porosity of microporous silicon films is described. The technique relies upon determination of film refractive index via measurement of the incident (Brewster) angle corresponding to a minimum in the intensity of light reflected from the air-film interface. The sample porosity is then obtained using an effective medium model. Porosities obtained using this method show general agreement with those obtained using gravimetric means and, where comparison was possible, excellent agreement with those of similarly-prepared films found by low angle X-ray reflectivity. These results confirm the general applicability of this technique to the determination of microporous silicon film porosity. (C) 2011 Elsevier B.V. All rights reserved.