This article presents the first thorough geochemical study of the tailings produced after processing and disposal of the Agios Filippos (Kirki, northeast Greece) high sulfidation epithermal deposit. The acid generation potential of the tailings was determined with the use of the acid/base accounting technique, and their toxicity was assessed with the toxicity characteristics leaching procedure (TCLP). The data derived from this study may be used: 1) in future geo-environmental modeling of high-sulfidation epithermal-type mineralization, 2) in forensic investigations aiming at identification of pollution sources, migration routes, mobility, fate and bio-available fractions of the most hazardous contaminants, and 3) during screening and selection of feasible remediation schemes in waste disposal sites.