Spin splittings in quantum wells have attracted considerable attention over the past decade due to potential application of semiconductor spin properties to "spintronic devices." Recent experimental results stimulate theoretical investigations of new physical situations like unconventional growth directions. Here we focus on electron spin properties in (110)-oriented quantum wells that are of particular interest because qualitative symmetry analysis shows that spin relaxation by the D'yakonov-Perel' mechanism should be strongly suppressed in this geometry. We combine symmetry analysis, envelope function theory, and tight-binding calculation and obtain quantitative description of the in-plane wave vector, well width, and applied electric field dependence of the spin structure of electron subbands in (110) quantum wells.