Abstract: Titanite occurs in the groundmass of a holocrystalline volcanic ejectum collected in the pyroclastic rocks of the Vico Volcanic complex at Tre Croci, near Viterbo, Italy. The host rock is composed of abundant K-feldspar and minor plagioclase, biotite, clinopyroxene and a feldspathoid (sodalite). Titanite is typically associated with zirconolite, biotite and Fe-oxides. It has a medium Al content (Al₂O₃ + Fe₂O₃ = 4–6 wt.%) and contains significant amounts of Zr and LREE, with a chondrite-normalised REE pattern similar to those of titanites from other alkaline rocks. Titanite has been corroded by fluids probably rich in dissolved F and P during a late alteration stage, with evidence for some remobilization and redistribution of the REE and actinide elements.