The paper presents an analytical treatment of double-diffusive nanofluid convection in a porous medium. The problem treated is natural convection past a vertical plate when the base fluid of the nanofluid is itself a binary fluid such as salty water. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis, while the Darcy model is used for the porous medium. In addition the thermal energy equations include regular diffusion and cross-diffusion terms. A similarity solution is presented.