Although the Mo(110) p(2x2)-S system has been widely studied, there have been no definitive studies that define the surface crystallography using modern methods. Sulfur was deposited on the clean Mo(110) surface from an in situ electrochemical source and the surface annealed to a coverage of 0.25 monolayer to produce a high-quality p(2 x 2) low-electron energy diffraction (LEED) pattern. Intensity-voltage curves from 13 nonequivalent beams were recorded at normal incidence using a video camera. These data were combined with tensor LEED calculations to produce an optimized surface structure. We allowed the coordinates of the Mo atoms in the first two substrate layers and the adsorbate S atom to vary until the Pendry R factor was minimized. There is evidence for adsorption-induced substrate reconstruction. The S adatom is located in a distorted central hollow (CH) site in which two of the top-layer Mo atoms have moved significantly outward. The top substrate layer is also rumpled on the order of 0.1-0.2 angstrom. The distortion is such that the final coordination of the S atom is somewhat closer to threefold coordination rather than the 2 + 2 coordination characteristic of of the undistorted CH site.