The crystal structure of (DMET)2BF4: 5,6-dihydro-2-(4,5-dimethyl-1,3-diselenol-2-ylidene)dithiolo[4,5-b] [1,4]dithiinium tetrafluoroborate (2:1), (C10H10S4Se2)2BF4, is determined. Crystal data: M(r) = 919.49, triclinic, P1, a = 7.032(2), b = 7.812(3), c = 27.502(11) angstrom, alpha = 90.87(2), beta = 90.28(2), gamma = 106.22(2)-degrees, V = 1450.5(15) angstrom3, Z = 2, D(x) = 2.11 Mg m-3, lambda(Mo K-alpha) = 0.71068 angstrom, mu = 5.60 mm-1, F(000) = 890, T = 297 K, R = 0.077 for 4600 reflections. Two crystallographically independent DMET molecules separately form columns along nearly perpendicular directions, and ordered BF4 anions are located between the DMET columns.