The first occurrence of britholite-(Ce) in Italy consists of small (0.2 mm) transparent pale blue hexagonal tabular crystals in volcanic ejecta, mainly composed of sanidine, from Monte Somma, Vesuvius. The mineral is hexagonal, space group P6 3/m (or P6 3) a = 9.597(9), c = 7.04(1) Å. The anhydrous crystal-chemical formula, derived from electron microprobe analysis, is: Ca 4(REE 3.1Ca 1.54Th 1.23U 0.08) 5.95(Si 5.42P 0.94) 6.36 O 26 with REE = Ce 1.77, La 0.70, Nd 0.47, Pr 0.16. Britholite-(Ce) from Monte Somma has a high calcium content and the highest thorium content so far reported for this mineral. It is uniaxial negative, with n ω = 1.772(2).