By means of high-resolution neutron powder diffraction (sample-limited resolution delta d/d greater than or equal to 10(-3), d = lattice spacing) the temperature dependence of the orthorhombic structure of the pseudosymmetric layer compound TlAu(CN)(2) was investigated in the range from 5 to 300 K in connection with optical measurements. No phase transition occurs, but similar to KAu(CN)(2), the longest lattice parameter b increases anomalously with decreasing temperature, from 30.460 Angstrom at 300 K to 30.851 Angstrom at 5 K. When the [Au(CN)(2)](-) ions are constrained to be linear, the b-lattice parameter increase is found to be due to the reduction of the angle between the [Au(3)(CN)(2)](-) ion and the b-axis, from 50.7 degrees at 300 K to 47.6 degrees at 5 K. Apart from these essential changes the results confirm the structure model of Blom et al., corresponding to space group Pbcn as derived previously from a single-crystal neutron diffraction measurement at room temperature. Short interatomic distances Au-Au approaching 3 Angstrom at 5 K indicate significant Au-Au overlap, causing (with Au-TI covalent overlap) the particular yellow color of TlAu(CN)(2).