We present data available on rare metal and indium distributions in cassiterite and associated minerals from thirteen Sn ± W granite-related ore deposits in the western Variscan Belt (Massif Central and Armorican Massif, France; Galicia, Spain; and SW England). Cassiterite and associated minerals including sulfides and titanium oxides were analysed using an electron probe microanalyzer (EPMA). Significant indium contents were only measured in cassiterite from hydrothermal vein-type mineralizations associated with peraluminous granites of Montbelleux, Abbaretz (French Armorican Massif) and Marcofán (Galicia); they correlate with the highest Nb, Ta and Fe substitutions. Two coupled substitutions are proposed: (1) 2 (Sn⁴⁺, Ti⁴⁺)↔(Fe³⁺, In ³⁺) + (Nb⁵⁺, Ta⁵⁺) and (2) Fe²⁺ + (Nb, Ta)⁵⁺ ↔ In ³⁺ + (Ti, Sn)⁴⁺ depending on Fe valence state. Sulfides (stannite, chalcopyrite, pyrite, arsenopyrite and sphalerite) and rutile associated with cassiterite contain significant amounts of indium, even when cassiterite is indium-free, suggesting preferential partitioning into the sulfides.