The local seismicity occurring at Campi Flegrei caldera during a recent unrest (1982--1984) has been modeled in terms of Coulomb stress changes due to magma chamber overpressure, superimposed on a background tensile regional stress. The computations, performed by a finite element method in heterogeneous axial-symmetric elastic models, also take into account the effects of the caldera structure on stress distribution. Coulomb stress changes have been obtained for the best oriented focal mechanisms, determined for the total applied stress, i.e., local change plus background regional stress. The results demonstrate a very good correlation between positive Coulomb stress changes and earthquake locations. Furthermore, there is a good agreement between observed focal mechanisms and the optimally oriented mechanisms as predicted by the model. The obtained results represent not only a fundamental contribution toward understanding mechanisms of seismic generation at Campi Flegrei and other calderas but also demonstrate that Coulomb stress changes in volcanic areas can be very effective, because of the high intensity, and deserve more attention than generally paid.