The fast ion conductor Ag3SBr is extremely difficult to prepare in stoichiometric proportion. Decomposition of the material at elevated temperatures precludes the creation of single crystals by the Bridgman method. Polycrystalline samples have previously been synthesized using the techniques of solid state reaction, crystallization from the melt, and precipitation from aqueous solution. However, subsequent X-ray diffraction or calorimetric measurements almost invariably suggest the presence of small quantities of unreacted AgBr. We investigate the effect of non-stoichiometry on the electrical properties of Ag3SBr. The transition temperature separating the superionic and covalent phases is not influenced by significant departure from stoichiometry. However, the magnitude of ionic conductivity in the superionic phase appears to be quite sensitive to the presence of unreacted AgBr.