We have studied the stress in porous silicon films as a function of depth and porosity using micro-Raman spectroscopy. Raman spectra were measured at different points along a cross section cleaved normal to the layer planes. Each spectrum was fitted using the phonon confinement model with the bulk phonon wavenumber as a free parameter. From the variation of this parameter we get the stress using the known dependence of phonon frequency on stress for bulk silicon. We observe a compressive stress at the interface with the substrate due to the lattice mismatch between porous and bulk silicon. The maximum value of the stress increases with porosity. The results obtained by Raman micro-spectroscopy agree well with the lattice mismatch measured by X-ray diffraction reported in the literature.