A probability distribution function for the fluctuations of the dissipative fluxes in simple viscous and heat-conducting fluids is proposed in the framework of extended irreversible thermodynamics. In equilibrium situations, this probability distribution function can be obtained in a direct way from the classical Einstein formula. For fluctuations near non-equilibrium steady states, the same results are shown to be valid by means of the Onsager-Machlup formalism. The stochastic noise in the evolution equations of the dissipative fluxes is also studied. & Co. • Berlin • New York. © Copyright by Walter de Gruyter & Co.