At present, the available procedures to determine optical parameters of tissue suffer from several limitations, either from a practical or a theoretical point of view, which restrict their use. The aim of the present study was to verify whether a single steady-state diffuse reflectance measurement could be exploited to estimate the optical characteristics of in vivo skin. Using integrating spheres, reflectance spectra of in vivo skin in different anatomical sites were measured. Further, transmittance of relatively thin structures (e.g., lobe of the ear) was measured at 633 and 800 nm. Results were compared with data obtained from a Monte Carlo model. As input parameters we used values of absorption and reduced scattering coefficients either estimated from previously determined in vitro data or calculated from reflectance and transmittance measurements. Analysis of results shows several peculiar features: (1) based upon the estimated set of absorption and reduced scattering coefficients, calculated diffuse reflectance spectrum matches well the experimental data, whereas intensity of light fluence in depth is underestimated; (2) the backward photon flux is strictly albedo dependent; (3) the in vivo scattering coefficient is lowered, with respect to the in vitro datum, by the presence of blood.