In general, internal cells are required to solve thermo-elastoplastic problems using a conventional boundary element method (BEM). However, in this case, the merit of BEM, which is the easy preparation of data, is lost. The conventional multiple-reciprocity boundary element method (MRBEM) cannot be used to solve the thermo-elastoplastic problems, because the distribution of initial strain or initial stress cannot be determined analytically. In this paper, it is shown that three-dimensional thermo-elastoplastic problems can be solved without the use of internal cells, by using the triple-reciprocity boundary element method. Initial strain formulations are adopted and the initial strain distribution is interpolated using boundary integral equations. A new computer program was developed and applied to several problems.