Gersdorffite, ideally NiAsS, and associated minerals from Contrada Zillì (Peloritani Mountains, Sicily, Italy) have been characterized through electron microprobe analysis and X-ray diffraction. Primary minerals, hosted in quartz veins, are represented by gersdorffite, tetrahedrite-(Fe), and chalcopyrite with minor pyrite and galena. Rare aikinite inclusions were observed in tetrahedrite-(Fe) and chalcopyrite. Gersdorffite occurs as euhedral to subhedral crystals, up to 1gmm in size, with (Sb,Bi)-enriched cores and (Fe,As)-enriched rims. Its chemical composition is (Ni0.79-0.95Fe0.18-0.04Co0.04-0.01)(As0.90-1.03Sb0.10-0.00Bi0.02-0.00)S0.98-0.92. It crystallizes in the space group P213, with unit-cell parameters aCombining double low line5.6968(7)gÅ, VCombining double low line184.88(7)gÅ3, and ZCombining double low line4, and its crystal structure was refined down to R1Combining double low line 0.035. Associated tetrahedrite-(Fe) has chemical formula (Cu5.79Ag0.07)ς5.86(Cu3.96Fe1.59Zn0.45)ς6.00(Sb3.95As0.17Bi0.03)ς4.15S13.06, with unit-cell parameters aCombining double low line 10.3815(10)gÅ, VCombining double low line1118.9(3)gÅ3, and space group I-43m. Its crystal structure was refined to R1Combining double low line0.027. Textural and crystallographic data suggest a polyphasic crystallization of gersdorffite under low-temperature conditions.