An analytic solution is derived for the potential generated by a current dipole source located in a three-dimensional insulated volume conductor with rectangular cross section. The solution is first obtained from an eigenfunction expansion for a point current source in the volume with Neumann boundary conditions. A distributed volume current sink is introduced to maintain continuity of charge within the volume. The dipole potential is obtained directly from the point source potential and is shown to be reducible to a doubly infinite summation. An algorithm is presented for modifying the summation to achieve the most rapid convergence dependent on the specific geometry of the problem.