The crystal structure and composition of (Sc1-x)Sc4Co6Sn18 (x = 0.14) were refined from single crystal X-ray diffraction data. The structure is disordered microtwinned tetragonal, I41/acd, a = 13.341(8), c = 26.69(2) Å, V = 4749.8 Å3, Z = 8, Dx = 7.58 g cm-3, Mr = 2708.5, μ = 23.85 mm-1, 73 refined parameters, R = 0.0638 for 1639 observed unique reflections with F0 > 4σ(F0). The title compound belongs to a large series of stannides with formula (M1-xSnx)-M4M'6Sn18 (M = rare earth, M' = Co, Ru, Rh, Ir, Os) and two related structures (tetragonal phase II with cell parameters a ≈ 13.7, c ≈27.4 Å and pseudo-cubic phase IF (earlier sometimes called phase III) with a ≈ 13.7 Å, which was explained as microtwinned phase II). The crystal was microtwinned. The refined volume fractions of three twin domains were 0.381(7), 0.287(7) and 0.332(7), respectively. A microtwinning of phase II seems to be an intrinsic feature of its structure thus reducing the probability of the forma-tion of the ideal cubic structure IF during the crystal growth.