During hot working processes of metals, precise knowledge of parameters such as strain, strain rate and temperature, is of prime importance for a true prediction of subsequent structural changes in the processed materials. This paper outlines the effect of starting porosity on the true strain generated in 316 L stainless steel powder precompacts during hot deformation by axisymmetric compression tests. The study was carried out at constant temperature, using cylindrical samples with starting porosities of 13 and 37%. Results have shown that below a certain ideal porosity of 22%, the true uniform strain in the central region remote from the specimen ends is always higher than the nominal mean applied strain. However, if the starting porosity is above 22%, then the true uniform strain generated in the central region of the deformed specimen is always lower than the nominal mean applied strain. But if the starting porosity is about 22%, then the true uniform strain is equal to the nominal applied mean strain. Empirical equations designed to quantify this true strain are proposed. These equations which are a function of the deformation variables can be very useful for computationnal purposes in controlled hot working operations of powder preforms. (c) 2007 Elsevier B.V. All rights reserved.