The initial stages of disilane Si2H6 reactive deposition on Ni(977) to form silicon nanowires have been examined using scanning tunneling microscopy. The effects of disilane exposure and dosing rate on the length distributions of the resulting silicon nanowires are discussed. Creating such atomically-wide structures using reactive deposition on stepped metal templates has potential applications in "bottom-up" nanofabrication technologies, especially in the preparation of massively parallel, aligned, and high aspect ratio structures.