A new polymorph of the title compound, (C₈H₂₀N₂)[TlBr₅], contains cations located about crystallographic centres of inversion and trigonal-bipyramidal anions which have a C₂ axis passing through the equatorial plane of the anion. The anion has the least distorted geometry seen so far in any structure possessing this anion and the axial Tl-Br bonds are about 0.13 Å longer than the equatorial Tl-Br bonds, consistent with related structures. The anion in the initially reported polymorph has lower symmetry and a greater distortion of the trigonal-bipyramidal coordination.