The determination of accurate and reliable basic physical properties of Be stars is a very complicated task which, among other things, requires a good knowledge of the variability pattern of each particular object. Possible confusion between a rotationally distorted photosphere and a pseudophotosphere – an inner optically thick part of a gradually formed envelope which temporarily mimics a photosphere – is discussed in some detail in relation to the stellar effective temperature, brightness and rate of rotation. It is shown that the currently available data allow us to set relatively stringent limits on possible radii of at least some brighter Be stars, but very few direct determinations of mass have been made. The only exceptions are the Be stars in eclipsing binaries. The trouble is, however, that all of them are interacting binaries for which reliable orbital solutions are seriously hampered by the presence of gas streams and by strong interactions between the binary components. Moreover, their masses need not be representative for the whole population of Be stars.
An answer to the question about the evolutionary stage of Be stars is even more uncertain since it is closely related to the principal, as yet unanswered question about the origin of the Be phenomenon itself.