The oxidation of reduced chlorides (MCl2) or chloride-hydrides (MClHx) of the lanthanides with sulfur (700-850 °C, 7 d, sealed tantalum capsules or evacuated silica vessels) usually results in the formation of the sesquisulfides M2S3 as the main products. In the presence of appropriate fluxes (e.g., alkali halides), the products often are obtained as single crystals, and the flux decides which modification is favoured. Ternary halides of the trivalent lanthanides with the corresponding alkali metal can mostly be found as the second components. Crystal growth and structural investigations of thus produced single crystals of Pr2S3 (from PrClH0.67 + S + NaCl, 5:5:1, A type: orthorhombic, Pnma (No. 62), Z = 4, a = 748.22(5), b = 405.51(3), c = 1560.74(9) pm, R = 0.024, Rw = 0.020), Ho2S3, (from U - Ho2S3, + KI, 1:1, D type: monoclinic, P21/m (No. 12), Z = 6, a = 1746.15(9), b = 400.23(3), c = 1012.43(6) pm, β = 98.529(4)°, R = 0.041, Rw = 0.035), and Yb2S3 (from T-Yb2S3 + KI, 1:1, E type: trigonal, R3̄c (No. 167), Z = 6, a = 674.97(2), c = 1820.11(9) pm, R = 0.019, Rw = 0.018) are reported here. In accordance with the lanthanide contraction, the trivalent cations (M3+) exhibit sulfur coordination numbers of 7 and 8 in A -Pr2S3, 6 and 7 in D -Ho2S3, and 6 in E -Yb2S3 (corundum-type structure).