The authors examine densitometric diagnostics by photonic absorption for the in-vivo determination of bone mass. Based on an analysis of the literature a comparison is made for values for accuracy, repeatability, and dosimetry offered by techniques such as single-energy photon absorptiometry (SPA), dual photon absorptiometry (DPA), dual-energy X-ray absorptiometry (DXA), or quantitative computer tomography (QCT). Also discussed are economic aspects and daily management, recent developments and future possibilities. None of the densitometric diagnostics examined is capable of entirely satisfying the different needs of measurement, and nearly all of the methods of photonic absorption reported here have specific indications. The coexistence of different systems will increase the priority of the definition of standardized protocols of calibration, so as to obtain densitometric data that may be compared.