We have developed a formalism for the transverse current correlation function in a binary fluid mixture, based on the generalised Langevin equation and Mori's continued fraction approach. The calculated numerical results show good agreement with the simulation results and the predicted time correlation function for the transverse current reproduces the hydrodynamic limit at small wave vectors and shows a negative minimum at large wave vectors. (C) 2003 Elsevier Science B.V. All rights reserved.