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A thallium-bearing variety of the lead&#8315;antimony oxysulfosalt chovanite from the Monte Arsiccio mine (Apuan Alps, Tuscany, Italy) has been reexamined. It occurs as thin, ribbon-like crystals, black in color, up to 5 mm in length in vugs of dolomite &#177; baryte &#177; quartz veins embedded in the metadolostone of the Sant&#8217;Olga level. Associated minerals are rouxelite, robinsonite, sphalerite, valentinite, baryte, dolomite, quartz, and Ba-rich K-feldspar. Chemical analysis pointed to contents of Tl up to 0.86 apfu, corresponding to the ideal chemical formula TlPb₂₆(Sb,As)₃₁S₇₂O. The structural role of thallium has been investigated using single-crystal X-ray diffraction using synchrotron radiation (&#955; = 0.59040 &#197;). Thallium-rich chovanite is monoclinic, space group <i>P</i>2₁/<i>c</i>, with unit-cell parameters <i>a</i> = 34.280(3), <i>b</i> = 8.2430(7), <i>c</i> = 48.457(4) &#197;, &#946; = 106.290(4)&#176;, and <i>V</i> = 13143(2) &#197;³. The crystal structure was refined to a final <i>R</i>₁ = 0.083 for 12,052 reflections with <i>F</i>_o &gt; 4&#963;(<i>F</i>_o) and 1210 refined parameters. The general features of thallium-rich chovanite agree with those of chovanite. Thallium is present as Tl⁺; it is disordered among two mixed (Pb/Tl) positions, with a Tl/Pb atomic ratio below 1, that precludes this compound to be a new species.