Abstract : A theoretical investigation was made for the determination of the three dimensional stress field of a cracked plate, of an arbitrary thickness, 2h, and subjected to a uniform external load of mode I. The displacement and stress fields are expressed in terms of the displacement V projected onto the plane containing the crack. In addition the question of uniqueness is examined for a whole class of these three-dimensional crack problems. It is found that solutions to such problems in elastostatics are unique, provided they satisfy the condition of local finite energy everywhere. Finally, it is shown that the solution is complete and it appears that at the corner, where the crack front meets the free surface of the plate, the solution is not separable either in spherical or cylindrical coordinates. (Author)