This paper reports an analytical and numerical study of the combined Soret and thermosolutal effects on natural convection in a vertical rectangular cavity filled with a binary mixture. Neumann boundary conditions for temperature and solute are applied to the vertical walls of the enclosure, while the two horizontal ones are assumed impermeable and insulated. The governing parameters for the problem are the thermal Rayleigh number, Ra-T, the Lewis number Le, the buoyancy ratio phi, the solute flux imposed on the vertical boundaries j, the Prandtl number Pr, the aspect ratio of the cavity A, and the integer number a (a = 0 for double diffusive convection and a = 1 for the coexistence of double diffusion convection and Soret effect). For convection in a thin vertical layer (A >> 1), analytical solutions for the stream function, temperature, and solute fields are obtained using a parallel flow approximation in the core region of the cavity and an integral form of the energy and constituent equations. Numerical solutions of the full governing equations are obtained for a wide range of the governing parameters. A good agreement is observed between the analytical model and the numerical simulations.