We have measured the Raman spectrum of porous silicon layers for different light polarizations. For the polarizations where the first-order Raman peak is forbidden in bulk silicon, porous silicon shows a band. This band is almost as intense as the one in the allowed polarizations but its lineshape is very different. The ‘forbidden’ band is usually wider and shifted to lower energies with respect to the allowed band. Both bands are analyzed in terms of sample characteristics, layer depth, and excitation wavelength.