The integral analysis of multilayered planar structures owes its high efficiency to the excellent matching of the Spectral Domain Approach (SDA) to the planar nature of the problem. This highly efficient approach is strongly encroached upon when arbitrary three-dimensional (3-D) surfaces in a multilayered environment have to be analyzed. However, for 3-D structures that consist of horizontal and strictly vertical conducting surfaces, the analytical possibilities of the SDA can be exploited further. The integral equation formulation is adapted to the geometry by expressing it in a hybrid dyadic-mixed potential form. The solution is improved with a combined spectral-spatial domain approach, where part of the reaction integrals are done in closed form in the spectral domain. This modified method avoids most theoretical and numerical problems, while the majority of practical 3-D problems in stratified media can still be handled.